<PAGE>   1
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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM 10-Q


(Mark one)
 [X] QUARTERLY REPORT UNDER SECTION 13 OR 15(d) OF THE SECURITIES
     EXCHANGE ACT OF 1934

     FOR THE QUARTERLY PERIOD ENDED SEPTEMBER 30, 1997
                                    -------------------
                                          OR

 [ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
     EXCHANGE ACT OF 1934

     For the transition period from _________________ to ________________

    COMMISSION FILE NO. 2-80930

                           DEL TACO RESTAURANT PROPERTIES I
                           a California limited partnership
                (Exact name of registrant as specified in its charter)

                  CALIFORNIA                                   95-3852699
        (State or other jurisdiction of                    (I.R.S. Employer
        incorporation or organization)                  Identification Number)

  23041 AVENIDA DE LA CARLOTA, SUITE 400, LAGUNA HILLS, CA        92653
         (Address of principal executive offices)               (Zip Code)

                                    (714) 462-9300
                 (Registrant's telephone number, including area code)

    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 
                                                      ---      ---

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<PAGE>   2
                                      INDEX

                        DEL TACO RESTAURANT PROPERTIES I
<TABLE>
<CAPTION>
PART I.  FINANCIAL INFORMATION                             PAGE NUMBER
<S>                                                              <C>
Item 1.  Financial Statements and Supplementary Data

Balance Sheets at September 30, 1997 (Unaudited) and
     December 31, 1996                                            3

Statements of Income for the three and nine months ended
     September 30, 1997 and 1996 (Unaudited)                      4

Statements of Cash Flows for the nine months ended
     September 30, 1997 and 1996 (Unaudited)                      5

Notes to Financial Statements                                     6


Item 2.  Management's Discussion and Analysis of
         Financial Condition and Results of Operations            9


PART II. OTHER INFORMATION

Item 6.  Exhibits and Reports on Form 8-K                        11


SIGNATURES                                                       12

</TABLE>


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<PAGE>   3
                        DEL TACO RESTAURANT PROPERTIES I

                                 BALANCE SHEETS
<TABLE>
<CAPTION>
                                                              September 30   December 31
                                                                  1997          1996
                                                               ----------    ----------
                                                              (Unaudited)
<S>                                                            <C>           <C>     
                                        ASSETS
CURRENT ASSETS:
  Cash                                                           $139,752      $130,996
  Receivable from General Partner (Note 4)                         44,442        38,478
  Deposits                                                            600           600
                                                               ----------    ----------
    Total current assets                                          184,794       170,074
                                                               ----------    ----------

PROPERTY AND EQUIPMENT, AT COST
  Land and improvements                                         1,852,482     1,852,482
  Buildings and improvements                                    1,013,134     1,013,134
  Machinery and equipment                                       1,136,026     1,136,026
                                                               ----------    ----------
                                                                4,001,642     4,001,642
  Less--accumulated depreciation                                1,661,372     1,628,543
                                                               ----------    ----------
                                                                2,340,270     2,373,099
                                                               ----------    ----------

                                                               $2,525,064    $2,543,173
                                                               ==========    ==========

                           LIABILITIES AND PARTNERS' EQUITY


CURRENT LIABILITIES:
  Payable to Limited Partners                                     $12,204       $11,319
  Accounts payable                                                  1,633         3,000
                                                               ----------    ----------
     Total current liabilities                                     13,837        14,319
                                                               ----------    ----------

PARTNERS' EQUITY
  Limited Partners                                              2,246,128     2,263,579
  General Partner-Del Taco, Inc.                                  265,099       265,275
                                                               ----------    ----------
                                                                2,511,227     2,528,854
                                                               ----------    ----------

                                                               $2,525,064    $2,543,173
                                                               ==========    ==========
</TABLE>

                             The accompanying notes are an
                       integral part of these financial statements



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<PAGE>   4
                        DEL TACO RESTAURANT PROPERTIES I

                              STATEMENTS OF INCOME

                                   (UNAUDITED)
<TABLE>
<CAPTION>
                                 THREE MONTHS ENDED      NINE MONTHS ENDED
                                    SEPTEMBER 30           SEPTEMBER 30
                                  1997        1996        1997        1996
                                --------    --------   ---------    --------
<S>                             <C>         <C>         <C>         <C>     
REVENUES:
  Rent (Notes 3 and 4)          $126,241    $120,783    $359,312    $334,752
  Interest                           814         705       2,595       1,823
  Other                            1,125          25       1,600         375
                                --------    --------    --------    --------
                                 128,180     121,513     363,507     336,950
                                --------    --------    --------    --------

EXPENSES:
  General and administrative       5,664       9,705      35,231      39,020
  Depreciation                    10,943      10,944      32,829      32,829
                                --------    --------    --------    --------
                                  16,607      20,649      68,060      71,849
                                --------    --------    --------    --------

Net income                      $111,573    $100,864    $295,447    $265,101
                                ========    ========    ========    ========

Net income per Limited
  Partnership Unit (Note 2)       $12.62      $11.41      $33.42      $29.99
                                ========    ========    ========    ========
</TABLE>


                     The accompanying notes are an integral
                      part of these financial statements.


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<PAGE>   5
                        DEL TACO RESTAURANT PROPERTIES I

                            STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)
<TABLE>
<CAPTION>
                                                     NINE MONTHS ENDED
                                                        SEPTEMBER 30
                                                      1997         1996
                                                   ---------     ---------
<S>                                                 <C>           <C>     
CASH FLOWS FROM OPERATING ACTIVITIES:

 Net income                                         $295,447      $265,101
 Adjustments to reconcile net income to net
  cash provided by operating activities:
    Depreciation                                      32,829        32,829
    Increase in payable to Limited Partners              885         2,265
    Increase in receivable from
     General Partner                                  (5,964)       (1,135)
    Decrease in accounts payable                      (1,366)         (355)
                                                   ---------     ---------

      Net cash provided by operating activities      321,831       298,705


CASH FLOWS FROM FINANCING ACTIVITIES:

 Cash distributions to partners                     (313,075)     (285,678)
                                                   ---------     ---------

Net increase in cash                                   8,756        13,027

Beginning cash balance                               130,996       115,012
                                                   ---------     ---------

Ending cash balance                                 $139,752      $128,039
                                                   =========     =========
</TABLE>



                     The accompanying notes are an integral
                       part of these financial statements.


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<PAGE>   6

                        DEL TACO RESTAURANT PROPERTIES I

                          NOTES TO FINANCIAL STATEMENTS

                               SEPTEMBER 30, 1997


NOTE 1 - BASIS OF PRESENTATION

The accompanying financial statements, some of which are unaudited, have been
prepared in accordance with generally accepted accounting principles for interim
financial information and with the instructions to Form 10-Q and Article 10 of
Regulation S-X. Accordingly, they do not include all of the information and
footnotes required by generally accepted accounting principles for complete
financial statements and should therefore be read in conjunction with the
financial statements and notes thereto contained in the Registrant's annual
report on Form 10-K for the year ended December 31, 1996. In the opinion of
management, all adjustments (consisting of normal recurring accruals) necessary
to present fairly the partnership's financial position at September 30, 1997,
the results of operations and cash flows for the nine month periods ended
September 30, 1997 and 1996 have been included. Operating results for the three
and nine months ended September 30, 1997 are not necessarily indicative of the
results that may be expected for the year ending December 31, 1997.

In fiscal 1996, the Registrant adopted Statement of Financial Accounting
Standards (SFAS) No. 121, "Accounting for the Impairment of Long Lived Assets
and for Long Lived Assets to be Disposed of." SFAS 121 requires that long-lived
assets be reviewed for impairment whenever events or changes in circumstances
indicate that the carrying value of the asset may not be recoverable. In
evaluating long-lived assets held for use, an impairment loss is recognized if
the sum of the expected future cash flows (undiscounted and without interest
charges) is less than the carrying value of the asset. Once a determination has
been made that an impairment loss should be recognized for long-lived assets,
various assumptions and estimates are used to determine fair value including,
among others, estimated costs of construction and development, recent sales of
comparable properties and the opinions of fair value prepared by independent
real estate appraisers. Long-lived assets to be disposed of are reported at the
lower of carrying amount or fair value less cost to sell.

The adoption of SFAS No. 121 did not have a material effect on the Registrant's
financial statements.



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<PAGE>   7

DEL TACO RESTAURANT PROPERTIES I
NOTES TO FINANCIAL STATEMENTS - CONTINUED
SEPTEMBER 30, 1997


NOTE 2 - NET INCOME PER LIMITED PARTNERSHIP UNIT

Net income per Limited Partnership Unit is based upon the weighted average
number of Units outstanding during the periods presented, which amounted to
8,751 in 1997 and 1996.

Pursuant to the Partnership Agreement, annual partnership net income is
allocated one percent to the General Partner and 99 percent to the Limited
Partners. A Partnership net loss in any year will be allocated 24 percent to the
General Partner and 76 percent to the Limited Partners until the losses so
allocated equal income previously allocated. Any additional losses will be
allocated one percent to the General Partner and 99 percent to the Limited
Partners. Partnership gains from any sale or refinancing will be allocated one
percent to the General Partner and 99 percent to the Limited Partners until
allocated gains and profits equal losses. Additional gains will be allocated 24
percent to the General Partner and 76 percent to the Limited Partners.

NOTE 3 - LEASING ACTIVITIES

The Registrant leases (the "Leases") certain properties (the "Properties") for
operation of restaurants to Del Taco, Inc. ("General Partner") on a triple net
basis. The Leases are for terms of 35 years commencing with the completion of
the restaurant facility located on each Property and require monthly rentals
equal to 12 percent of the gross sales of the restaurants. There is no minimum
rental under any of the Leases. The Registrant had a total of six Properties
leased as of September 30, 1997 and 1996, two of which have been subleased to
Del Taco franchisees (one of which is affiliated with Del Taco, Inc.)

For the three months ended September 30, 1997, the five restaurants operated by
Del Taco, for which the Registrant is the lessor, had combined, unaudited sales
of $891,056 and net income of $36,149 as compared to $866,137 and $36,213
respectively, for the corresponding period in 1996. Net income by restaurant
includes charges for general and administrative expenses incurred in connection
with supervision of restaurant operations and interest expense. For the three
months ended September 30, 1997, the one restaurant operated by a Del Taco
franchisee, for which the Registrant is the lessor, had unaudited sales of
$160,958 as compared with $140,410 during the same period in 1996.



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<PAGE>   8

DEL TACO RESTAURANT PROPERTIES I
NOTES TO FINANCIAL STATEMENTS - CONTINUED
SEPTEMBER 30, 1997


NOTE 3 - LEASING ACTIVITIES - (Continued)

For the nine months ended September 30, 1997, the five restaurants operated by
Del Taco, for which the Registrant is the lessor, had combined, unaudited sales
of $2,549,509 and net income of $87,122 as compared to $2,391,303 and $49,774
respectively, for the corresponding period in 1996. For the nine months ended
September 30, 1997, the one restaurant operated by a Del Taco franchisee, for
which the Registrant is the lessor, had unaudited sales of $444,767 as compared
with $398,309 during the same period in 1996.

For the three months and nine months ended September 30, 1997, the Elkhorn
Boulevard restaurant in Sacramento, California reported net losses of $2,619 and
$12,579 as compared to net losses of $3,710 and $11,925 respectively, for the
corresponding period in 1996.

NOTE 4 - TRANSACTIONS WITH DEL TACO

The receivable from General Partner consists primarily of rent accrued for the
month of September. The September rent receivable was collected on October 11,
1997.

Del Taco, Inc. serves in the capacity of general partner in other partnerships
which are engaged in the business of operating restaurants, and four
partnerships which were formed for the purpose of acquiring real property in
California for construction of Mexican-American restaurants for lease under
long-term agreements to Del Taco, Inc. for operation under the Del Taco trade
name.

In addition, see Note 5 with respect to certain distributions to the General
Partner.

NOTE 5 - DISTRIBUTIONS

On October 15, 1997, a distribution to the Limited Partners of $121,323 or
approximately $13.87 per Limited Partnership Unit, was approved. Such
distribution was paid on October 16, 1997. The General Partner also received a
distribution of $1,225 with respect to its 1% partnership interest.



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<PAGE>   9

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

Liquidity and Capital Resources

The Registrant commenced offering of Limited Partnership Units on March 21,
1983. By March 20, 1984, the sale of such Units provided a total capitalization
for the Registrant of $4,375,500. Fifteen percent of the cash received from the
sale of Limited Partnership Units was used to pay commissions to brokers and to
reimburse the General Partner for offering costs incurred. The remaining funds
were expended for the acquisition of sites and construction of six restaurants.
In 1985, the first four restaurants opened for business and two additional
restaurants were opened in 1986. Approximately $4,002,000 was expended for such
purposes.

Since the six restaurants owned by the Registrant opened, cash flow from Lease
payments received from Del Taco, the Registrant's General Partner, which leases
all six restaurants, has provided adequate liquidity for operation of the
Registrant. However, the Registrant's overwhelmingly predominant source of
income to meet its expenses and fund distributions to its Limited Partners is
payments from Del Taco under the Leases, comprising primarily rent calculated on
the basis of the gross sales of the restaurants operated on the Properties, as
to which there are no contractually specified minimum or guaranteed amounts.
Thus, the adequacy of the Registrant's liquidity and capital resources in the
future will depend primarily upon the gross revenues of such restaurants as well
as upon Del Taco's financial condition and results of operations generally.



                                      -9-
<PAGE>   10

Results of Operations

The Registrant owns six Mexican-American restaurants that are under long-term
lease to its General Partner for operation under the Del Taco trade name. The
Registrant receives rental revenues equal to 12 percent of restaurant sales. For
the three months ended September 30, rental revenues increased from $120,783 in
1996 to $126,241 in 1997. For the nine months ended September 30, rental
revenues increased from $334,752 in 1996 to $359,312 in 1997. Such changes in
rental revenue are directly attributable to changes in sales at the restaurants.

The following table sets forth rental revenue earned by restaurant for the
quarter and year to date:
<TABLE>
<CAPTION>
                                                  THREE MONTHS ENDED            NINE MONTHS ENDED
                                                     SEPTEMBER 30                 SEPTEMBER 30
                                                   1997          1996           1997           1996
                                                   ----          ----           ----           ----
<S>                                              <C>           <C>             <C>           <C>     
Riverside Avenue, Rialto, CA                     $ 21,458      $ 18,471        $ 59,580      $ 49,038

Elden Avenue, Moreno Valley, CA                    18,588        19,092          55,331        54,651

Foothill Boulevard, La Verne, CA                   26,865        26,481          77,744        74,136

Baseline & Archibald, Rancho                       19,315        16,847          53,372        47,797
  Cucamonga, CA

Elkhorn Boulevard, Sacramento, CA                  12,957        12,153          35,911        33,997

Haven Avenue, Rancho                               27,088        27,739          77,374        75,133
   Cucamonga, CA                                  -------       -------         -------       -------
  
       Total                                     $126,241      $120,783        $359,312      $334,752
                                                  =======       =======         =======       =======
</TABLE>


The following table sets forth the percentage relationship to total general and
administrative expenses of items included in the Registrant's Statements of
Income:
<TABLE>
<CAPTION>
                                                      Percentage of Total
                                                 General & Administrative Expense
                                                        Nine Months Ended
                                                           September 30
                                                        1997           1996
                                                        ----           ----
<S>                                                     <C>           <C>   
Accounting fees                                         40.62%        39.85%
Distribution of
  information to
  Limited Partners                                      57.11         57.15
Other                                                    2.27          3.00
                                                       ------        ------
                                                       100.00%       100.00%
</TABLE>

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<PAGE>   11

Operating expenses include general and administrative expenses which consist
primarily of accounting fees and costs of distribution of information to the
Limited Partners. For the three months ended September 30, general and
administrative expenses decreased from $9,705 in 1996 to $5,664 in 1997. The
quarter ended September 30, 1996 included printing costs for new checks,
envelopes and stationary. For the nine months ended September 30, general and
administrative expenses decreased from $39,020 in 1996 to $35,231 in 1997. For
the three months ended September 30, the Registrant incurred depreciation
expense in the amount of $10,943 in 1997 and $10,944 in 1996. The Registrant
incurred depreciation expense of $32,829 for nine months ended September 30,
1997 and 1996,respectively.

For the three months ended September 30, revenues increased by $6,667 while
expenses decreased by $4,042 resulting in an increase in net income from
$100,864 in 1996 to $111,573 in 1997. For the nine months ended September 30,
revenues increased by $26,557 while expenses decreased by $3,789 resulting in an
increase in the Registrant's net income from $265,101 for the nine months ended
September 30, 1996 to $295,447 for the corresponding period in 1997.

For the reasons stated under "Liquidity and Capital Resources" above, the
Registrant's results of operations in the future will depend primarily upon the
gross revenues of the restaurants located on the Properties leased to Del Taco
as well as upon Del Taco's financial condition and results of operations
generally.

PART II.  OTHER INFORMATION

Item 6. Exhibits and Reports on Form 8-K

(b) No reports on Form 8-K were filed during the nine months ended September 30,
    1997.

   27      Financial Data Schedule.

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<PAGE>   12

                                   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.


                                            DEL TACO RESTAURANT PROPERTIES I
                                            (a California limited partnership)
                                            Registrant

                                            Del Taco, Inc.
                                            General Partner



Date:  October 30, 1997                     /s/ Robert J. Terrano
                                            ---------------------
                                            Robert J. Terrano
                                            Executive Vice President,
                                            Chief Financial Officer


Date:  October 30, 1997                     /s/ C. Douglas Mitchell
                                            -----------------------
                                            C. Douglas Mitchell
                                            Vice President and Corporate
                                            Controller


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