The University of the District of Columbia, responding to criticism from Congress, has scaled down the size - but not the cost - of its proposed $70 million downtown campus.

In a revised master plan, approved unanimously yesterday by the D.C. City Council, the university said it had reduced by 25 per cent the number of students it expects to accomodate in its proposed new buildings.

But it said costs could not come down because of inflation and the need to provide better equipment and more space for individual students and faculty members.

"What we were doing before was cramming people in," said university vice president Claude Ford, who is in charge of planning. "Now we are going back to normal (college space) standards."

Last spring the General Accounting Office charged that because of enrollment projections that were far too high the new public university wanted to provide much more space than it needed.

Under an amendment proposed by Sen. Patrick J. Leahy (D-Vt.), Congress then voted to freeze $56.7 million in this year's budget to complete the downtown campus until the university and the city government came up with a new long-range master plan.

Yesterday the City Council approved the plan after receiving a letter of endorsement from Mayor Walter E. Washington.

It still requires approval from the Senate and House District appropriations subcommittees, headed by Leahy and Rep. William Natcher (D-Ky.), before the money can be spent.

Under the revised plan the university would be able to accommodate a total of 9,600 full-time equivalent students, divided between the proposed new campus just north of Mount Vernon Square and its uptown campus, already under construction, at Connecticut Avenue and Van Ness Street NW.

Until last week, when it submitted the revised plan, the university ahd said these buildings would accommodate about 12,800 full-time equivalent students. It said it expected that many - an increase of 48 percent over current enrollment - by 1983, when the buildings are scheduled to be completed.

This past year the university had a full-time equivalent enrollment of 8,725. The number was down about 10 percent from the 1975 total enrollment of the three insitutions that were merged to form the university - Federal City College, D.C. Teachers College and Washington Technical Institute.

In its report, GAO projected that the university would have 9,600 full-time equivalent students by 1983, the same capacity figure that the university offered in its new plan.

Full-time equivalent enrollment is computed by adding the total number of credit hours students are taking and dividing by 15, the number of credit hours in a full-time course load.

Yesterday Ford said the similarity in the figures was "absolutely coincidental." He said the new capacity figure was arrived at by using standard space formulas for college construction. Even with the additional space per student, Ford said UDC students would still be more crowded than those at most other colleges in the area.