<PAGE>   1
 
================================================================================
 
                                 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                   JUNE 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)
 
<TABLE>
<S>                                                          <C>
                         CALIFORNIA                                    95-3852699
               (STATE OR OTHER JURISDICTION OF                      (I.R.S. EMPLOYER
               INCORPORATION OR ORGANIZATION)                      IDENTIFICATION NO.)
 
    23041 AVENIDA DE LA CARLOTA, LAGUNA HILLS, CALIFORNIA                 92653
          (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                     (ZIP CODE)
</TABLE>
 

                                 (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  ___
 
================================================================================
<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 June 30, 1997 (Unaudited) and
     December 31, 1996                                           3

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

Statements of Cash Flows for the six months ended
     June 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>



                                      -2-

<PAGE>   3


                        DEL TACO RESTAURANT PROPERTIES I

                                 BALANCE SHEETS


<TABLE>
<CAPTION>

                                                   JUNE 30          December 31
                                                     1997               1996
                                                  -----------       -----------
                                                  (UNAUDITED)
                                     ASSETS
                                     ------
<S>                                                <C>                <C>       
CURRENT ASSETS:
  Cash                                             $  115,282         $  130,996
  Receivable from General Partner (Note 4)             43,986             38,478
  Deposits                                                600                600
                                                   ----------         ----------
    Total current assets                              159,868            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                    1,650,429          1,628,543
                                                   ----------         ----------
                                                    2,351,213          2,373,099
                                                   ----------         ----------

                                                   $2,511,081         $2,543,173
                                                   ==========         ==========


                        LIABILITIES AND PARTNERS' EQUITY
                        --------------------------------

CURRENT LIABILITIES:
  Payable to Limited Partners                      $   11,359         $   11,319
  Accounts payable                                      1,146              3,000
                                                   ----------         ----------
     Total current liabilities                         12,505             14,319
                                                   ----------         ----------

PARTNERS' EQUITY
  Limited Partners                                  2,233,604          2,263,579
  General Partner-Del Taco, Inc.                      264,972            265,275
                                                   ----------         ----------
                                                    2,498,576          2,528,854
                                                   ----------         ----------

                                                   $2,511,081         $2,543,173
                                                   ==========         ==========
</TABLE>



                          The accompanying notes are an
                   integral part of these financial statements



                                      -3-


<PAGE>   4






                        DEL TACO RESTAURANT PROPERTIES I
                        --------------------------------
                              STATEMENTS OF INCOME
                              --------------------
                                   (UNAUDITED)
                                   -----------

<TABLE>
<CAPTION>
                                        THREE MONTHS ENDED                 SIX MONTHS ENDED
                                             JUNE 30                            JUNE 30
                                       1997             1996             1997             1996
                                     --------         --------         --------         --------
<S>                                  <C>              <C>              <C>              <C>
REVENUES:
  Rent (Notes 3 and 4)               $122,154         $111,986         $233,071         $213,969
  Interest                                757              489            1,781            1,118
  Other                                   400              200              475              350
                                     --------         --------         --------         --------
                                      123,311          112,675          235,327          215,437
                                     --------         --------         --------         --------

EXPENSES:
  General and administrative            8,760            9,260           29,567           29,315
  Depreciation                         10,943           10,942           21,886           21,885
                                     --------         --------         --------         --------
                                       19,703           20,202           51,453           51,200
                                     --------         --------         --------         --------

Net income                           $103,608         $ 92,473         $183,874         $164,237
                                     ========         ========         ========         ========

Net income per Limited
  Partnership Unit (Note 2)          $  11.72         $  10.46         $  20.80         $  18.58
                                     ========         ========         ========         ========
</TABLE>






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



                                      -4-

<PAGE>   5






                        DEL TACO RESTAURANT PROPERTIES I
                        --------------------------------
                            STATEMENTS OF CASH FLOWS
                            ------------------------
                                   (UNAUDITED)
                                   -----------

<TABLE>
<CAPTION>

                                                             SIX MONTHS ENDED
                                                                  JUNE 30
                                                           1997               1996
                                                        ---------          ---------
<S>                                                     <C>                <C>      
CASH FLOWS FROM OPERATING ACTIVITIES:

Net income                                              $ 183,874          $ 164,237
Adjustments to reconcile net income to net
  cash provided by operating activities:
    Depreciation                                           21,886             21,885
    Increase in payable to Limited
     Partners                                                  40              1,508
    Decrease in receivable from
     General Partner                                       (5,508)              (587)
    Decrease in accounts payable                           (1,854)              (907)
                                                        ---------          ---------

      Net cash provided by operating activities           198,438            186,136


CASH FLOWS FROM FINANCING ACTIVITIES:

 Cash distributions to partners                          (214,152)          (195,669)
                                                        ---------          ---------

Net decrease in cash                                      (15,714)            (9,533)

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

Ending cash balance                                     $ 115,282          $ 105,479
                                                        =========          =========

</TABLE>







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


                                      -5-


<PAGE>   6



                        DEL TACO RESTAURANT PROPERTIES I
                        --------------------------------
                          NOTES TO FINANCIAL STATEMENTS
                          -----------------------------
                                  JUNE 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 June 30, 1997, the
results of operations and cash flows for the six month periods ended June 30,
1997 and 1996 have been included. Operating results for the three and six months
ended June 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 of fair value less cost to sell.

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

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.


                                      -6-

<PAGE>   7

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

NOTE 2 - NET INCOME PER LIMITED PARTNERSHIP UNIT - (CONTINUED)

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 June 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 June 30, 1997, the five restaurants operated by Del
Taco, for which the Registrant is the lessor, had combined, unaudited sales of
$867,749 and net income of $29,141 as compared to $799,554 and $11,196
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 June 30, 1997, the one restaurant operated by a Del Taco
franchisee, for which the Registrant is the lessor, had unaudited sales of
$150,201 as compared with $133,663 during the same period in 1996.




                                      -7-

<PAGE>   8



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


NOTE 3 - LEASING ACTIVITIES - (CONTINUED)

For the six months ended June 30, 1997, the five restaurants operated by Del
Taco, for which the Registrant is the lessor, had combined, unaudited sales of
$1,658,449 and net income of $50,973 as compared to $1,525,176 and $13,561
respectively, for the corresponding period in 1996. For the six months ended
June 30, 1997 the one restaurant operated by a Del Taco franchisee, for which
the Registrant is the lessor, had unaudited sales of $283,809 as compared with
$257,899 during the same period in 1996.

For the three months, and six months ended June 30, 1997, the Elkhorn Boulevard
restaurant in Sacramento, California reported net losses of $5,394 and $9,960 as
compared to net losses of $3,655 and $8,215 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 June. The June rent receivable was collected on July 10, 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 July 12, 1997, a distribution to the Limited Partners of $97,934 or
approximately $11.19 per Limited Partnership Unit, was approved. Such
distribution was paid on July 23, 1997. The General Partner also received a
distribution of $989 with respect to its 1% partnership interest.



                                      -8-


<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 June 30, rental revenues increased from $111,986 in 1996
to $122,154 in 1997. For the six months ended June 30, rental revenues increased
from $213,969 in 1996 to $233,071 in 1997. Such increases in rental revenue are
directly attributable to increases 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                 SIX MONTHS ENDED
                                                    JUNE 30                          JUNE 30
                                             1997            1996              1997              1996
                                             ----            ----              ----              ----
<S>                                       <C>              <C>              <C>              <C>     
Riverside Avenue, Rialto, CA              $ 20,553         $ 16,365         $ 38,123         $ 30,567

Elden Avenue, Moreno Valley, CA             19,430           18,695           36,772           35,560

Foothill Boulevard, La Verne, CA            26,105           24,721           50,879           47,655

Baseline & Archibald, Rancho                18,024           16,040           34,057           30,948
  Cucamonga, CA

Elkhorn Boulevard, Sacramento, CA           12,380           11,374           22,954           21,844

Haven Avenue, Rancho                        25,662           24,791           50,286           47,395
                                          --------         --------         --------         --------
  Cucamonga, CA

          Total                           $122,154         $111,986         $233,071         $213,969
                                          ========         ========         ========         ========
</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
                                          --------------------------------
                                                  Six Months Ended
                                                       June 30
                                           1997                     1996
                                          -------                  -------
<S>                                        <C>                      <C>   
Accounting fees                            61.96%                   53.04%
Distribution of
  information to
  Limited Partners                         35.33                    42.96
Other                                       2.71                     4.00
                                          ------                   ------
                                          100.00%                  100.00%
</TABLE>



                                      -10-


<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 June 30, general and administrative
expenses decreased from $9,260 in 1996 to $8,760 in 1997. For the six months
ended June 30, general and administrative expenses increased from $29,315 in
1996 to $29,567 in 1997. For the three months ended June 30, the Registrant
incurred depreciation expense in the amount of $10,942 in 1996 and $10,943 in
1997. The Registrant incurred depreciation expense of $21,885 and $21,886 for
six months ended June 30, 1996 and 1997,respectively.

For the three months ended June 30, revenues increased by $10,636 while expenses
decreased by $499 resulting in an increase in net income from $92,473 in 1996 to
$103,608 in 1997. For the six months ended June 30, revenues increased by
$19,890 while expenses increased by $253 resulting in an increase in
Registrant's net income from $164,237 for the six months ended June 30, 1996 to
$183,874 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 six months ended 
         June 30, 1997.

27       Financial Data Schedule.



                                      -11-


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


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



                                      -12-