<PAGE>   1
                                   FORM 10-Q
                       SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C.  20549

                   QUARTERLY REPORT UNDER SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

               FOR THE QUARTERLY PERIOD ENDED SEPTEMBER 30, 1998

                         COMMISSION FILE NUMBER 0-13465



                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
             (Exact name of registrant as specified in its charter)




            MARYLAND                                          52-1358879
  (State or other jurisdiction                             (I.R.S. Employer
of incorporation or organization)                         Identification No.)




                       9200 KEYSTONE CROSSING, SUITE 500
                        INDIANAPOLIS, INDIANA 46240-7602
                    (Address of principal executive offices)
                                   (Zip Code)


                                 (317) 817-7500
              (Registrant's telephone number, including area code)

                                 NOT APPLICABLE
              (Former name, former address and former fiscal year,
                         if changed since last report.)


Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.

Yes   X         No
    -----          -----
<PAGE>   2
PART 1 - FINANCIAL INFORMATION

ITEM 1 - FINANCIAL STATEMENTS

                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                        STATEMENTS OF FINANCIAL POSITION


<TABLE>
<CAPTION>
                                                                                      September 30,
                                                                                           1998               December 31,
                                                                                       (Unaudited)                 1997
                                                                                    -----------------         -------------

                              ASSETS
                              ------
<S>                                                                                     <C>                     <C>
Cash and cash equivalents                                                                  $    2,070             $   26,125
Investments in and advances to Local Limited Partnerships (Note 2)                          1,814,207              1,780,933
                                                                                            ---------              ---------

                                                                                           $1,816,277             $1,807,058
                                                                                            =========              =========

                  LIABILITIES AND PARTNERS' EQUITY (DEFICIT)
                  ------------------------------------------

Liabilities:
      Administrative and reporting fee payable to General Partner (Note 3)                 $  894,758             $  829,964
      Due to General Partner (Note 3)                                                           6,315                  6,315
      Accrued interest on partner loans (Note 3)                                                  514                  -
      Accrued expenses                                                                         69,308                 40,210
                                                                                            ---------              ---------

                                                                                              970,895                876,489
                                                                                            ---------              ---------

Partners' equity (deficit):
      General Partner -- The National Housing Partnership (NHP)                               (86,911)               (86,059)
      Original Limited Partner -- 1133 Fifteenth Street Associates                            (91,811)               (90,959)
      Other Limited Partners -- 11,519 investment units                                     1,024,104              1,107,587
                                                                                            ---------              ---------

                                                                                              845,382                930,569
                                                                                            ---------              ---------

                                                                                           $1,816,277             $1,807,058
                                                                                            =========              =========
</TABLE>





                       See notes to financial statements.

                                      -1-
<PAGE>   3



                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                            STATEMENTS OF OPERATIONS
                                  (UNAUDITED)


<TABLE>
<CAPTION>

                                                                       Three Months Ended                Nine Months Ended
                                                                          September 30,                     September 30,
                                                                -----------------------------     ------------------------------
                                                                    1998             1997             1998               1997
                                                                ------------     ------------     ------------       -----------
<S>                                                             <C>            <C>                 <C>            <C>
REVENUES:
   Share of profits from Local Limited
    Partnerships (Note 2)                                         $   2,600        $     -         $   33,274          $     -
   Distributions and repayments received in excess
    of investment in Local Limited Partnerships                         -                -                -               11,686
   Interest income                                                      106               70              276                709
                                                                   --------         --------        ---------           --------

                                                                      2,706               70           33,550             12,395
                                                                   --------         --------        ---------           --------

COSTS AND EXPENSES:
   Share of losses from Local Limited
    Partnerships (Note 2)                                             -               22,239            -                 53,803
   Administrative and reporting fees to
    General Partner (Note 3)                                         21,598           21,598           64,794             64,794
   Interest on Partner loans                                            178              311              514                892
   Other operating expenses                                          26,870           10,706           53,429             34,988
                                                                   --------         --------        ---------           --------

                                                                     48,646           54,854          118,737            154,477
                                                                   --------         --------        ---------           --------

NET LOSS                                                          $ (45,940)       $ (54,784)      $  (85,187)         $(142,082)
                                                                   ========         ========        =========           ========

NET LOSS ASSIGNABLE TO
   LIMITED PARTNERS                                               $ (45,022)       $ (53,688)      $  (83,483)         $(139,240)
                                                                   ========         ========        =========           ========

NET LOSS PER LIMITED
   PARTNERSHIP INTEREST                                           $      (4)       $      (5)      $       (7)         $     (12)
                                                                   ========         ========        =========           ========
</TABLE>





                       See notes to financial statements.

                                      -2-
<PAGE>   4

                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                    STATEMENT OF PARTNERS' EQUITY (DEFICIT)
                     NINE MONTHS ENDED SEPTEMBER 30, 1998
                                  (UNAUDITED)


<TABLE>
<CAPTION>
                                         The National         1133
                                           Housing         Fifteenth          Other
                                         Partnership         Street          Limited
                                            (NHP)          Associates        Partners          Total
                                         -----------       ----------        --------          -----
<S>                                        <C>              <C>            <C>               <C>
Equity (deficit) at January 1, 1998        $(86,059)        $(90,959)      $1,107,587        $ 930,569

Net loss -- nine months ended
  September 30, 1998                           (852)            (852)         (83,483)         (85,187)
                                            -------          -------        ---------         --------

Equity (deficit) at September 30, 1998     $(86,911)        $(91,811)      $1,024,104        $ 845,382
                                            =======          =======        =========         ========

Percentage interest at
 September 30, 1998                               1%               1%              98%             100%
                                            =======          =======        =========         ========
                                                (A)              (B)              (C)
</TABLE>

(A)      General Partner
(B)      Original Limited Partner
(C)      Consists of 11,519 investment units





                       See notes to financial statements.

                                      -3-
<PAGE>   5



                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                            STATEMENTS OF CASH FLOWS
                                  (UNAUDITED)


<TABLE>
<CAPTION>
                                                                                Nine Months Ended September 30,     
                                                                        --------------------------------------------
                                                                                 1998                   1997
                                                                               ---------             ----------
<S>                                                                          <C>                    <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
   Distributions received in excess of investment in
    Local Limited Partnerships                                                $      -              $    11,686
   Interest received                                                                 276                    709
   Operating expenses paid                                                       (24,331)               (45,408)
                                                                               ---------             ----------

Net cash used in operating activities                                            (24,055)               (33,013)

CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD                                    26,125                 62,193
                                                                               ---------             ----------

CASH AND CASH EQUIVALENTS, END OF PERIOD                                      $    2,070            $    29,180
                                                                               =========             ==========

RECONCILIATION OF NET LOSS TO NET
   CASH USED IN OPERATING ACTIVITIES:
    Net loss                                                                  $  (85,187)           $  (142,082)
                                                                               ---------             ----------
    Adjustments to reconcile net loss to net cash
      used in operating activities:
         Share of (profits) losses from Local Limited
            Partnerships                                                         (33,274)                53,803
            Increase in administrative and reporting fees payable                 64,794                 64,794
            Increase in accrued interest on Partner loans                            514                    892
            Increase (decrease) in other accrued expenses                         29,098                (10,420)
                                                                               ---------             ----------

               Total adjustments                                                  61,132                109,069
                                                                               ---------             ----------

      Net cash used in operating activities                                   $  (24,055)           $   (33,013)
                                                                               =========             ==========
</TABLE>





                       See notes to financial statements.

                                      -4-
<PAGE>   6
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                         NOTES TO FINANCIAL STATEMENTS



(1)      ACCOUNTING POLICIES

         ORGANIZATION

         National Housing Partnership Realty Fund I (the "Partnership") is a
         limited partnership organized under the laws of the State of Maryland
         under the Maryland Revised Uniform Limited Partnership Act on October
         21, 1983. The Partnership was formed for the purpose of raising
         capital by offering and selling limited partnership interests and then
         investing in limited partnerships ("Local Limited Partnerships"), each
         of which owns and operates an existing rental housing project which is
         financed and/or operated with one or more forms of rental assistance
         or financial assistance from the U.S.  Department of Housing and Urban
         Development ("HUD").

         The General Partner raised capital for the Partnership by offering and
         selling to additional limited partners 11,519 investment units. The
         Partnership acquired limited partnership interests ranging from 98% to
         99% in ten Local Limited Partnerships, each of which was organized to
         acquire and operate an existing rental housing project.

         On June 3, 1997, Apartment Investment and Management Company, a
         Maryland corporation ("AIMCO" and, together with its subsidiaries and
         other controlled entities, the "AIMCO Group"), acquired all of the
         issued and outstanding capital stock of NHP Partners, Inc., a Delaware
         corporation ("NHP Partners"), and the AIMCO Group acquired all of the
         outstanding interests in NHP Partners Two Limited Partnership, a
         Delaware limited partnership ("NHP Partners Two"). The Acquisition was
         made pursuant to a Real Estate Acquisition Agreement, dated as of May
         22, 1997 (the "Agreement"), by and among AIMCO, AIMCO Properties,
         L.P., a Delaware limited partnership (the "Operating Partnership"),
         Demeter Holdings Corporation, a Massachusetts corporation ("Demeter"),
         Phemus Corporation, a Massachusetts corporation ("Phemus"), Capricorn
         Investors, L.P., a Delaware limited partnership ("Capricorn"), J.
         Roderick Heller, III and NHP Partners Two LLC, a Delaware limited
         liability company ("NHP Partners Two LLC"). NHP Partners owns all of
         the outstanding capital stock of the National Corporation for Housing
         Partnerships, a District of Columbia corporation ("NCHP"), which is
         the general partner of The National Housing Partnership, a District of
         Columbia limited partnership ("NHP"). Together, NCHP and NHP Partners
         Two own all of the outstanding partnership interests in the NHP. NHP
         is the general partner of National Housing Partnership Realty Fund I
         (a Maryland Limited Partnership) (the "Registrant"). As a result of
         these transactions, the AIMCO Group has acquired control of the
         general partner of the Registrant and, therefore, may be deemed to
         have acquired control of the Registrant.

         The Original Limited Partner of the Partnership is 1133 Fifteenth
         Street Associates, whose limited partners were key employees of NCHP
         at the time the Partnership was formed and whose general partner is
         NHP.

         BASIS OF PRESENTATION

         The accompanying unaudited interim financial statements reflect all
         adjustments which are, in the opinion of management, necessary to a
         fair statement of the financial condition and results of operations
         for the interim periods presented. All such adjustments are of a
         normal and recurring nature.

         While the General Partner believes that the disclosures presented are
         adequate to make the information not misleading, it is suggested that
         these financial statements be read in conjunction with the financial
         statements and notes included in NHP Realty Fund I's Annual Report
         filed in Form 10-K for the year ended December 31, 1997.





                                      -5-
<PAGE>   7
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                         NOTES TO FINANCIAL STATEMENTS



(2)      INVESTMENTS IN AND ADVANCES TO LOCAL LIMITED PARTNERSHIPS

         The Partnership owns a 98% limited partnership interest in Gates Mills
         I Limited Partnership and 99% limited partnership interests in nine
         other Local Limited Partnerships. Because the Partnership, as a
         limited partner, does not exercise control over the activities of the
         Local Limited Partnerships in accordance with the partnership
         agreements, the investments in Local Limited Partnerships are
         accounted for using the equity method. Thus, the investments (and the
         advances made to the Local Limited Partnerships as discussed below)
         are carried at cost plus the Partnership's share of the Local Limited
         Partnerships' profits less the Partnership's share of the Local
         Limited Partnerships' losses and distributions. However, because the
         Partnership is not legally liable for the obligations of the Local
         Limited Partnerships, and is not otherwise committed to provide
         additional support to them, it does not recognize losses once its
         investments, reduced for its share of losses and cash distributions,
         reach zero in each of the individual Local Limited Partnerships. As of
         September 30, 1998 and December 31, 1997, investments in eight of the
         ten Local Limited Partnerships had been reduced to zero. As a result,
         the Partnership did not recognize $1,086,400 and $1,184,908 of losses
         from Local Limited Partnerships during the nine months ended September
         30, 1998 and 1997, respectively. As of September 30, 1998 and December
         31, 1997, the Partnership has not recognized a total of $16,896,913
         and $15,810,513, respectively, of its allocated share of cumulative
         losses from the Local Limited Partnerships in which its investment is
         zero.

         Advances made by the Partnership to the individual Local Limited
         Partnerships are considered part of the Partnership's investment in
         Local Limited Partnerships. When advances are made to a Local Limited
         Partnership for which the Partnership carries its investment at zero,
         they are charged to operations as a loss on investment in the Local
         Limited Partnership using previously unrecognized cumulative losses.
         As discussed above, due to the cumulative losses incurred by eight of
         the Local Limited Partnerships, the aggregate balance of investments
         in and advances to Local Limited Partnerships, for these eight Local
         Limited Partnerships, has been reduced to zero at September 30, 1998
         and December 31, 1997. To the extent these advances are repaid by the
         Local Limited Partnerships in the future, the repayments will be
         credited as distributions in excess of investment in Local Limited
         Partnerships. These advances are carried as a payable to the
         Partnership by the Local Limited Partnerships.

         During the nine months ended September 30, 1998 and 1997, no working
         capital advances or repayments were made between the Partnership and
         the Local Limited Partnerships. The combined amount carried as due to
         the Partnership by the Local Limited Partnerships was $376,951 as of
         September 30, 1998.

         The following are combined statements of operations for the three and
         nine months ended September 30, 1998 and 1997, respectively, of the
         Local Limited Partnerships in which the Partnership has invested. The
         statements are compiled from financial statements of the Local Limited
         Partnerships, prepared on the accrual basis of accounting, as supplied
         by the management agents of the projects, and are unaudited.





                                      -6-
<PAGE>   8
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
                         NOTES TO FINANCIAL STATEMENTS



                       COMBINED STATEMENTS OF OPERATIONS


<TABLE>
<CAPTION>
                                            Three Months Ended                  Nine Months Ended
                                                September 30,                      September 30,
                                      -------------------------------    ------------------------------
                                            1998             1997             1998             1997
                                      --------------    -------------    -------------    -------------
<S>                                    <C>              <C>               <C>              <C>
Rental income                           $ 1,812,455      $ 1,815,518      $ 5,461,468      $ 5,472,074
Other income                                 64,820           57,007          172,154          151,063
                                         ----------       ----------       ----------       ----------

   Total income                           1,877,275        1,872,525        5,633,622        5,623,137
                                         ----------       ----------       ----------       ----------

Operating expenses                        1,434,218        1,386,852        3,995,550        4,036,389
Interest, taxes and insurance               600,824          694,567        1,817,813        1,948,491
Depreciation                                291,244          296,250          886,981          892,159
                                         ----------       ----------       ----------       ----------

   Total expenses                         2,326,286        2,377,669        6,700,344        6,877,039
                                         ----------       ----------       ----------       ----------

Net loss                                $  (449,011)     $  (505,144)     $(1,066,722)     $(1,253,902)
                                         ==========       ==========       ==========       ==========

National Housing Partnership
  Realty Fund I share of losses         $  (443,415)     $  (499,037)     $(1,053,126)     $(1,238,711)
                                         ==========       ==========       ==========       ==========
</TABLE>


(3)    TRANSACTIONS WITH THE GENERAL PARTNER

         During the nine month periods ended September 30, 1998 and 1997, the
         Partnership accrued administrative and reporting fees payable to the
         General Partner in the amount of $64,794 for services provided to the
         Partnership. The Partnership did not make any payments to the General
         Partner for these fees during each of the respective periods. The
         amount due the General Partner by the Partnership for administrative
         and reporting fees was $894,758 and $829,964 at September 30, 1998 and
         December 31, 1997, respectively.

         During the nine months ended September 30, 1998 and 1997, no working
         capital advances or repayments were made between the General Partner
         and the Partnership. The amount owed to the General Partner at
         September 30, 1998 and December 31, 1997, was $6,315. Interest is
         charged on borrowings at the Chase Manhattan Bank rate of prime plus
         2%. Chase Manhattan Bank prime was 8.5% at September 30, 1998. Accrued
         interest on this loan amounted to $514 and zero at September 30, 1998
         and December 31, 1997, respectively. There can be no assurance that
         the General Partner will continue to advance such funds to the
         Partnership.

         The advances and accrued administrative and reporting fees payable to
         the General Partner will be paid as cash flow permits or from proceeds
         generated from the sale or refinancing of one or more of the
         underlying properties of the Local Limited Partnerships.





                                      -7-
<PAGE>   9




ITEM 2 -     MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
             AND RESULTS OF OPERATIONS

                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)


The Private Securities Litigation Reform Act of 1995 provides a "safe harbor"
for forward-looking statements in certain circumstances. Certain information
included in this Report and other Partnership filings (collectively "SEC
Filings") under the Securities Act of 1933, as amended, and the Securities
Exchange Act of 1934, as amended (as well as information communicated orally or
in writing between the dates of such SEC Filings) contains or may contain
information that is forward-looking, including statements regarding the effect
of government regulations. Actual results may differ materially from those
described in the forward-looking statements and will be affected by a variety
of factors including national and local economic conditions, the general level
of interest rates, terms of governmental regulations that affect the
Partnership and interpretations of those regulations, the competitive
environment in which the properties owned by the Local Limited Partnerships
operate, the availability of working capital and dispositions of properties
owned by the Partnership.

YEAR 2000 COMPLIANCE

General Description of the Year 2000 Issue and the Nature and Effects of the
Year 2000 on Information Technology (IT) and Non-IT Systems

The Year 2000 Issue is the result of computer programs being written using two
digits rather than four to define the applicable year.  The Partnership is
dependent upon the General Partner and its affiliates for management and
administrative services ("Managing Agent").  Any computer programs or hardware
that have date-sensitive software or embedded chips may recognize a date using
"00" as the year 1900 rather than the year 2000.  This could result in a system
failure or miscalculations causing disruptions of operations, including, among
other things, a temporary inability to process transactions, send invoices, or
engage in similar normal business activities.

The Managing Agent has determined that it will be required to modify or replace
significant portions of its software and certain hardware so that those systems
will properly utilize dates beyond December 31, 1999. The Managing Agent
presently believes that with modifications or replacements of existing software
and certain hardware, the Year 2000 Issue can be mitigated.  However, if such
modifications and replacements are not made, or are not completed timely, the
Year 2000 Issue could have a material impact on the operations of the Managing
Agent and the Partnership.

Status of Progress in Becoming Year 2000 Compliant

The Managing Agent's plan to resolve the Year 2000 Issue involves the following
four phases: assessment, remediation, testing and implementation.  To date, the
Managing Agent has fully completed its assessment of all information systems
that could be significantly affected by the Year 2000, and has begun the
remediation, testing and implementation phase on both hardware and software
systems.  Assessments are continuing in regards to embedded systems in
operating equipment.  The Managing Agent anticipates having all phases complete
by June 1, 1999.

In addition to the areas the Partnership is relying on the Managing Agent to
verify compliance with,  the Partnership has certain operating equipment,
primarily at the property sites,  which needed to be evaluated for Year 2000
compliance.  The focus of the General Partner was to the security systems,
elevators, heating-ventilation-air-conditioning systems, telephone systems and
switches, and sprinkler systems. The General Partner is currently engaged in
the identification of all non-compliant operational systems, and is in the
process of estimating the costs associated with any potential modifications or
replacements needed to such systems in order for them to be Year 2000
compliant.  It is not expected that such costs would have a material adverse
affect upon the operations of the Partnership.





                                      -8-
<PAGE>   10
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
          MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                           AND RESULTS OF OPERATIONS




Risk Associated with the Year 2000

The General Partner believes that the Managing Agent has an effective program
in place to resolve the Year 2000 issue in a timely manner and has appropriate
contingency plans in place for critical applications that could affect the
Partnership's operations.   To date, General Partner is not aware of any
external agent with a Year 2000 issue that would materially impact the
Partnership's results of operations, liquidity or capital resources.  However,
the General Partner has no means of ensuring that external agents will be Year
2000 compliant.  The  General Partner does not believe that the inability of
external agents to complete their Year 2000 resolution process in a timely
manner will have a material impact on the financial position or results of
operations of the Partnership.  However, the effect of non-compliance by
external agents is not readily determinable.

LIQUIDITY AND CAPITAL RESOURCES

The properties in which the Partnership has invested, through its investments
in the Local Limited Partnerships, receive one or more forms of assistance from
Federal, state or local governments or agencies. As a result, the Local Limited
Partnerships' ability to transfer funds either to the Partnership or among
themselves in the form of cash distributions, loans or advances is generally
restricted by these government-assistance programs. These restrictions may
impact the Partnership's ability to meet its cash obligations.

For the past several years, various proposals have been advanced by the United
States Department of Housing and Urban Development ("HUD"), Congress and others
proposing the restructuring of HUD's rental assistance programs under Section 8
of the United States Housing Act of 1937 ("Section 8"), under which 1,213
units, 77 percent of the total units owned by the properties in which the
Partnership has invested, receive rental subsidies. These subsidies are
generally provided pursuant to project-based Housing Assistance Payment
Contracts ("HAP Contracts") between HUD and the owners of the properties. On
October 27, 1997, the President signed into law the Multifamily Assisted
Housing Reform and Affordability Act of 1997 (the "1997 Housing Act"). Under
the 1997 Housing Act, the mortgage financing and HAP contracts of certain
properties assisted under Section 8, with rents above market levels and
financed with HUD-insured mortgage loans, will be restructured by adjusting
subsidized rents to market levels, thereby reducing subsidy levels, and
lowering required debt service costs as needed to ensure financial viability at
the reduced rents and subsidy levels. The 1997 Housing Act retains
project-based subsidies for most properties (properties in rental markets with
limited supply, properties serving the elderly, and certain other properties).

The 1997 Housing Act phases out project-based subsidies on selected properties
servicing families not located in rental markets with limited supply,
converting such subsidies to a tenant-based subsidy. Under a tenant-based
system, rent vouchers would be issued to qualified tenants who then could elect
to reside at properties of their choice, provided the tenant has the financial
ability to pay the difference between the selected property's monthly rent and
the value of the voucher, which would be established based on HUD's regulated
fair market rent for the relevant geographical areas. The 1997 Housing Act
provides that properties will begin the restructuring process in federal fiscal
year 1999 (beginning October 1, 1998), and that HUD will issue final
regulations implementing 1997 Housing Act on or before October 27, 1998.
Congress has elected to renew HAP Contracts expiring before October 1, 1998 for
one year terms, generally at existing rents, so long as the properties remain
in compliance with the HAP Contracts. While the Partnership does not expect the
provisions of the 1997 Housing Act to result in a significant number of tenants
relocating from properties owned by the Local Limited Partnerships, there can
be no assurance that the provisions will not significantly affect the
operations of the properties of the Local Limited Partnerships. Furthermore,
there can be no assurance that other changes





                                      -9-
<PAGE>   11
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
          MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                           AND RESULTS OF OPERATIONS




in Federal housing subsidy policy will not occur. Any such changes could have
an adverse effect on the operation of the Partnership.

Net cash used in operations for the nine months ended September 30, 1998 was
$24,055 as compared to cash used in operations of $33,013 for the nine months
ended September 30, 1997. The decrease in cash used in operations resulted from
a decrease in operating expenses paid, partially offset by a decrease in
distributions received in excess of investment in Local Limited Partnerships.

During the nine months ended September 30, 1998 and 1997, no working capital
advances or repayments were made between the Partnership and the Local Limited
Partnerships. The combined amount carried as due to the Partnership by the
Local Limited Partnerships was $376,951 as of September 30, 1998.

Distributions received from Local Limited Partnerships represent the
Partnership's proportionate share of the excess cash available for distribution
from the Local Limited Partnerships. As a result of the use of the equity
method of accounting for the Partnership's investments, as of September 30,
1998, investments in eight Local Limited Partnerships had been reduced to zero.
For these investments, cash distributions received are recorded in income as
distributions received in excess of investment in Local Limited Partnerships.
For those investments not reduced to zero, distributions received are recorded
as distributions from Local Limited Partnerships. There were no cash
distributions during the nine months ended September 30, 1998. Cash
distributions of $11,686 were received during the nine months ended September
30, 1997. The receipt of distributions in future quarters and years is
dependent upon the operations of the underlying properties of the Local Limited
Partnerships to generate sufficient cash for distribution in accordance with
applicable HUD regulations.

Cash and cash equivalents amounted to $2,070 at September 30, 1998. The ability
of the Partnership to meet its on-going cash requirements, in excess of cash on
hand at September 30, 1998, is dependent upon the future receipt of
distributions from the Local Limited Partnerships or proceeds from sales or
refinancing of one or more of the underlying properties of the Local Limited
Partnerships. The General Partner will continue to manage the Partnership's
assets prudently in an effort to achieve positive cash flow and will evaluate
lending the Partnership additional funds as such funds are needed, but is in no
way legally obligated to make such loans.

During the nine months ended September 30, 1998 and 1997, no working capital
advances or repayments were made between the General Partner and the
Partnership. The amount owed to the General Partner at September 30, 1998 and
December 31, 1997, was $6,315.  Interest is charged on borrowings at the Chase
Manhattan Bank rate of prime plus 2%. Chase Manhattan Bank prime was 8.5% at
September 30, 1998. Accrued interest on this loan amounted to $514 and zero at
September 30, 1998 and December 31, 1997, respectively. There can be no
assurance that the General Partner will continue to advance such funds to the
Partnership.

At September 30, 1998, the Partnership owes the General Partner $894,758 for
administrative and reporting services performed. The payment of the unpaid
administrative and reporting fees will most likely result from the sale or
refinancing of the underlying properties of the Local Limited Partnerships,
rather than through recurring operations.

Eight of the Local Limited Partnerships in which the Partnership has invested
have deferred acquisition notes. With the exception of Fairmeadows and
Southridge, these notes have matured or will reach final maturity prior to
December, 1999. These notes are secured by both the Partnership's and NHP's
interests in the Local Limited Partnerships. In the event of a default on the
notes, the note holders would be able to assume NHP's and the Partnership's
interests in the Local Limited Partnerships.





                                      -10-
<PAGE>   12
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
          MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                           AND RESULTS OF OPERATIONS




Griffith Limited Partnership has defaulted on its deferred acquisition note and
related accrued interest which became due on October 31, 1997, which raises
substantial doubt about the Local Limited Partnership's ability to continue as
a going concern with its present ownership structure. The Local Limited
Partnership's continued existence as a going concern with its present ownership
structure is dependent on the ability to repay, refinance, restructure, or
renegotiate this note. The General Partner is currently negotiating to extend
the note and maintain ownership of the property. Should no agreement be reached
and the note matures absent a sale or refinancing which produces sufficient
funds to repay the note in full, a default would occur on the note. Such
default could lead to a foreclosure by the note holder of the security
underlying the note such that the Partnership may lose its interest in the
Griffith Limited Partnership. Should the Partnership lose its interest in
Griffith Limited Partnership, partners in the Partnership may incur adverse tax
consequences. The impact of the tax consequences is dependent upon each
partner's individual tax situation.

Southward Limited Partnership has a deferred acquisition note and related
accrued interest which came due on October 4, 1998 and Northgate Village
Limited Partnership has a deferred acquisition note and related accrued
interest due on July 26, 1999, which raises substantial doubt about the Local
Limited Partnerships' ability to continue as going concerns with their present
ownership structure. The Local Limited Partnerships' continued existence as
going concerns with their present ownership structure is dependent on the
ability to repay, refinance, restructure, or renegotiate these notes. Should no
agreement be reached and the notes mature absent any sales or refinancing which
produce sufficient funds to repay the notes in full, a default would occur on
the notes. Such defaults could lead to a foreclosure by the note holders of the
security underlying the notes such that the Partnership may lose its interests
in the Local Limited Partnerships. Should the Partnership lose its interests in
the Local Limited Partnerships, partners in the Partnership may incur adverse
tax consequences. The impact of the tax consequences is dependent upon each
partner's individual tax situation.

San Jose Limited Partnership, Gates Mills I Limited Partnership and Hurbell IV
Limited Partnership have deferred acquisition notes and related accrued
interest due on August 29, 1999, October 1, 1999 and November 9, 1999,
respectively. Should the notes mature absent any sales or refinancing which
produce sufficient funds to repay the notes in full, a default would occur on
the notes. Such defaults could lead to a foreclosure by the note holders of the
security underlying the notes such that the Partnership may lose its interests
in the Local Limited Partnerships. Should the Partnership lose its interests in
the Local Limited Partnerships, partners in the Partnership may incur adverse
tax consequences. The impact of the tax consequences is dependent upon each
partner's individual tax situation.

RESULTS OF OPERATIONS

The Partnership has invested as a limited partner in Local Limited Partnerships
which operate ten rental housing properties. In prior years, results of
operations of NHP Realty Fund I were significantly impacted by the
Partnership's share of the losses of the Local Limited Partnerships. These
losses included depreciation and accrued deferred acquisition note interest
expense which are noncash in nature. Eight of the ten investments in Local
Limited Partnerships have been reduced to zero. As a result, the Partnership's
operations are no longer being affected by its share of the operations from
these eight partnerships. The Partnership has recorded its share of operations
in the remaining two Local Limited Partnerships which amounted to profits of
$33,274 for the nine months ended September 30, 1998, and losses of $53,803 for
the nine months ended September 30, 1997.

The Partnership realized a net loss of $85,187 for the nine months ended
September 30, 1998, compared to a net loss of $142,082 for the nine months
ended September 30, 1997. Net loss per unit of other limited partnership
interest decreased from $12 to $7 for the 11,519 units outstanding for both
periods. The decrease in net loss was primarily due to the Partnerships' share
of profits from Local Limited Partnerships of $33,274 recognized in 1998,
compared to the Partnerships' share of losses from Local Limited Partnerships
of $53,803 recognized in 1997, partially offset by an increase in operating
expenses. During the nine months ended September 30, 1998, the Partnership
incurred operating expenses of





                                      -11-
<PAGE>   13
                   NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                        (A MARYLAND LIMITED PARTNERSHIP)
          MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                           AND RESULTS OF OPERATIONS




approximately $53,400 related to complying with SEC filing, auditing, and
reporting and mailing requirements. The Partnership did not recognize
$1,086,400 of its allocated share of losses from eight Local Limited
Partnerships for the nine months ended September 30, 1998, as the Partnership's
net carrying basis in these Local Limited Partnerships had been reduced to
zero. The Partnership's share of operating losses from the Local Limited
Partnerships, if not limited to its investment account balance, would have
decreased $185,585 between periods, primarily due to a decrease in operating
expenses.

The Partnership realized a net loss of $45,940 for the three months ended
September 30, 1998, compared to a net loss of $54,784 for the three months
ended September 30, 1997. Net loss per unit of other limited partnership
interest decreased from $5 to $4 for the 11,519 units outstanding for both
periods. The decrease in net loss was primarily due to the Partnerships' share
of profits from Local Limited Partnerships of $2,600 recognized in 1998,
compared to the Partnerships' share of losses from Local Limited Partnerships
of $22,239 recognized in 1997, partially offset by an increase in operating
expenses. During the three months ended September 30, 1998, the Partnership
incurred operating expenses of approximately $16,500 related to complying with
SEC filing, auditing, and reporting and mailing requirements. The Partnership
did not recognize $446,015 of its allocated share of losses from eight Local
Limited Partnerships for the three months ended September 30, 1998, as the
Partnership's net carrying basis in these Local Limited Partnerships had been
reduced to zero. The Partnership's share of operating losses from the Local
Limited Partnerships, if not limited to its investment account balance, would
have decreased $55,622 between periods, primarily due to a decrease in
operating expenses.

PART II - OTHER INFORMATION

ITEM 6  -  EXHIBITS AND REPORTS ON FORM 8-K

         (a)     Exhibits

                 Exhibit No.

                 27       Financial Data Schedule.





                                      -12-
<PAGE>   14


                                   SIGNATURES



         Pursuant to the requirements of the Securities Exchange Act of 1934,
the registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.



                             NATIONAL HOUSING PARTNERSHIP REALTY FUND I
                             ------------------------------------------
                             (Registrant)


                             By:  The National Housing Partnership,
                                  its sole General Partner
                                 
                                 
                             By:  National Corporation for Housing
                                  Partnerships, its sole General Partner
                                 
                                 
                                 
November 13, 1998            By:                   /s/
-----------------                 -------------------------------------------
                                  Troy D. Butts
                                  As Senior Vice President and Chief Financial
                                     Officer





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