WASHINGTON (AP) _ Mayor Marion Barry today delivered a list of concessions from University of the District of Columbia trustees to students seeking their resignations. But he refused to reveal the concessions publicly.

The protest forced cancellation of classes at the city-run university for the third day today.

Barry met with a majority of the board members today after agreeing on Thursday to ask 11 of the 15 board members to resign by March 31. The mayor also conveyed the students' request that two of the board members resign immediately.

Barry said at the end of a 4 1/2 -hour negotiating session Thursday that he is powerless to force the trustees to resign.

The students claim the board has taken a number of actions that have threatened the quality of education at UDC, a public institution with an enrollment of about 12,000.

The students initially wanted board Chairwoman Nira H. Long and the board's student representative, Cynthia Smith, to resign immediately.

But today, Mark Thomas, a protest leader, said students are willing to meet with Smith to dicuss her situation.

Students took over a campus building Wednesday, saying they were upset about several trustee actions, including a plan to spend $1.6 million for renovations to a library so a controversial artwork, ''The Dinner Party,'' can be installed there.

Employees were allowed in the buildings this morning so they could carry out necessary physical functions.

Feminist artist Judy Chicago is donating the ceramic sculpture, which depicts the history of women in 39 place settings, some containing images of female genitalia.

Students said the money could be better spent in improving academic programs. Several UDC departments have had problems maintaining their accreditations.

The students on Wednesday also seized control of another building housing offices of the school's top administrators, but left it after the administrators and others agreed to leave, UDC spokesman John Britton said.

Estimates of the number of students involved in the protest have ranged from 100 to 1,000.

The school's Faculty Senate, which has disagreed with the school's administration on a number of issues in recent years, backed the students, who also want an improved athletic program, compliance with education standards set by a regional accreditation board and an increased emphasis on an African- American curriculum.

Barry said he believed the students had legitimate concerns, especially since the school has had five presidents or acting presidents in the last eight years.