Clark University in Worcester will divest of all its stock in companies doing business in racially separated South Africa by 1988 if apartheid is not abolished, the school's trustees have voted.

Meanwhile, trustees at Smith College, concluding a two-day campus meeting in Northampton, voted Saturday for partial divestiture.

"Many U.S. corporations have been exemplary in their conduct of business within the Union of South Africa, and their voices have contributed to the discussion of the need to eliminate apartheid," Richard P. Traina, president of Clark, said in a statement Saturday.

"At the same time, these companies are necessarily powerless in effecting the degree of change required to end the oppression that is taking place," Traina added.

The Clark trustees set May 31, 1987, and June 30, 1988, as target dates for selling stock, depending on the degree companies adhere to the Sullivan Principles in trying to promote equal hiring of blacks in South Africa, said Alicia Ianiere, assistant communications director.

Ms. Ianiere said she had no figures of dollar amounts of the school's endowment that would be affected by the divestiture policy.

The Smith trustees voted to divest immediately from corporations that have not signed the Sullivan Principles. The move would affect two or three corporations, less than one percent, or $1.9 million, of the school's total endowment fund of $207 million, according to Suzinne Pak, a senior and chairwoman of the student-faculty Ethical Investment Committee.

Ms. Pak said the trustees voted to retain stock in corporations adhering to the Sullivan Principles but to divest from banks lending money to South Africa. She said the school will also increase its current number of scholarships to South African non-whites from two to four.

"The committee, as well as the entire student campus, is very disappointed at the response of the trustees," said Ms. Pak, referring to students demanding total divestment.

Meanwhile Saturday, students at Tufts University in Medford held a rally outside the quarterly meeting of the university's trustees to protest the board's decision not to divest of South African-related investments.

The 40 students and others protested in silence, their mouths covered with tape, as trustees entered the meeting.

"We're frustrated with the lack of student voice in this decision," said senior Laura Streitfeld. "We don't just want to protest. We want to communicate."