Georgetown University's trustees have voted to liquidate the university's investments in companies doing business in South Africa that fail to adopt the Sullivan Principles -- a voluntary code of conduct designed to improve conditions for black South African workers.

In their Thursday vote, which set no timetable, the trustees also committed the university to divesting itself of holdings in companies that have adopted the principles but fail to adhere to them and give no satisfactory explanation.

Of about $15 million Georgetown has invested in companies doing business in South Africa, about $2 million is in companies that have not subscribed to the principles, a university spokeswoman said last night. The names of the companies could not be learned immediately.

As of February, 135 companies, including almost all major U.S. employers in South Africa, were listed as signatories to the principles, developed in 1977 by a veteran civil rights activist, the Rev. Leon H. Sullivan. Signatories pledge to desegregate their facilities and pay equal wages to blacks and others.

Georgetown's move comes amid increasing nationwide attempts to bring about change in South Africa's apartheid policy of racial segregation.

In a statement issued yesterday, Georgetown said that instead of setting a fixed date for divestiture, the board "would rather divest after determining that the companies in which the university has invested are unwilling to sign the principles, or having signed them are unwilling to adhere to them."

The commitments on divestiture came as part of a 15-point resolution adopted by the board on policy toward South Africa. Among other things, it calls for ultimate divestiture of investments in companies supplying the South African military and police, and for exploration of South African issues through academic programs.

The board acted on a proposal submitted by a committee of Georgetown students, faculty and administrators.