The trustees of the University of the District of Columbia, under pressure from the D.C. Council and Mayor Marion Barry, yesterday endorsed the establishment of a law school at UDC, but said they would set it up only "if feasible."

Last year the board rejected a proposal to take over the Antioch School of Law, on 16th Street NW, which is scheduled to close next spring. They said the cost of the law school would damage UDC, whose own enrollment problems forced a 10 percent faculty layoff in September.

The D.C. Council voted in October 1986 to rescue Antioch by transforming it into a city-financed school that would become part of UDC in three years. The council placed the new law school under an interim five-member board of governors.

The board members said their action, approved on a 12-to-0 vote, was a step in carrying out an agreement in July between Barry and the council. The mayor said he would stop trying to block the new law school if the council dropped its requirement that Antioch faculty members be employed by the new public law school and that UDC be allowed to take it over immediately.

Board Chairman N. Joyce Payne said UDC expects to hire a consultant soon to conduct a feasibility study in line with requirements of the American Bar Association, which accredits law schools. If the study determines that there is a demand for such a school and indicates that its costs could be borne by the university, she said, the board then would decide definitely to move ahead with it.

Antioch leaders voted to close the school in May 1986, citing financial and accreditation problems. At the time, the school had 362 students. It now has just one third year class of 80 students.

UDC President Rafael Cortada said that "once we get the results of the feasibility study, and assuming that it is feasible, then we will proceed."

In an interview, Thomas J. Mack, a former Antioch Law School dean who now heads the interim board, said there is no need for such a feasibility study. "We feel it's been studied endlessly," Mack said. "The community wanted this law school and there was an overwhelming vote by the council."

The interim board has placed advertisements seeking applicants for the dean's chair, and Mack said it plans to recruit students for next fall. The interim board also has hired seven former Antioch professors to continue the school's legal aid programs for which participating students receive course credits.

The UDC board also asked the mayor and council to give it immediate control over $4.1 million appropriated for the school, which is now in the hands of the law school's interim board of governors.

"It is important that those funds be under the control of the UDC board," said Payne. Another UDC board member, Herbert O. Reid, complained that the interim governors "are spending that money at a rate as fast as possible."