The trustees of the University of the District of Columbia turned down a proposed takeover of Antioch Law School last night, saying the high cost of the move would damage the university.

The 8-to-4 vote followed an emotional debate and reversed a board resolution in March that endorsed acquiring the innovative, 14-year-old school, which has been beset by financial and accreditation problems.

The school at 2633 16th St. NW is affiliated with Antioch University of Yellow Springs, Ohio, whose trustees have threatened to close the law school because they are no longer able to support it. Last night Thomas J. Mack, the law school's interim dean, said no first-year class would be admitted in the fall and that the school would be phased out by 1988.

"I'm very disappointed," said Mack. "I think the community will have a tremendous gap in two years. But I think we were treated very fairly."

D.C. City Council member Hilda Mason (Statehood-At Large) said she would introduce legislation soon for the District to rescue the school by making it an independent public institution with its own board of trustees.

But Mack said he doubted whether the council would agree to that. "UDC was a great option" for the law school, he said. "But it was the last of the options available."

Before last night's vote, Trustee Nira Long said a study by a special UDC committee indicated that the law school would require about $7 million in city funds during the first 15 months after a UDC takeover. In late March, based on figures provided by Antioch, the board was told that the full cost of acquiring the school, which had 362 students this year, would be $2 million.

"A law school would be an asset if we could afford it," said Trustee Thomas A. Hart. "But to jump into something like this is irresponsible. The cost is so much higher than any figure" given before. In mid-March the council added $1.3 million for the takeover to next year's city budget.

Earlier at last night's meeting the board voted 6 to 5 to lay off 63 of the university's 735 nonfaculty employes, for a savings of $1.7 million. The action complies with a City Council mandate last year to reduce administrative costs that have remained relatively high at UDC since the school was created by a merger of three previous city institutions nine years ago.

Next year the university, which is losing enrollment, is facing cutbacks in its teaching staff.

"In the wake of the reduction in force of our staff how can we take on all the Antioch employes?" asked Trustee Joseph Webb.

"And I'm afraid the American Bar Association said we will have little policy control over this institution."

ABA evaluators have proposed removing Antioch Law's accreditation because of deficiencies in facilities, finances and academic standards, but the ABA has postponed final action.

The school operates as a public interest law firm with students required to get one-third of their credits by handling cases for low-income clients.

Trustee Daniel Fivel said last night that Antioch has "a fantastic record of public interest and public service. If you let this institution die you will have the death of the most dedicated young people and the most dedicated faculty for the cause of humanity that we have in this country. We are dealing with a moral decision. If you are worried about the money, let the mayor and the council decide that."

Voting against the Antioch takeover were Long, Hart, Webb, Lucy Cohen, F.D.R. Fox, Concha Johnson, Herbert O. Reid and Virginia Howard. Besides Fivel, the Rev. Raymond Kemp, Peter Edelman and Robert King voted for the takeover.