NORTHAMPTON, Mass. (AP) _ Students demanding that Smith College divest from companies doing business in South Africa occupied the administration building for a fifth day today, and four Brown University students fasted for a second day in protest of that school's investments.

Euphemia H. Steffey, chairwoman of Smith's trustees, was to arrive today at the 2,500-student women's college in western Massachusetts, and a group of trustees is to meet next week to review investment criteria.

College spokeswoman Ann Shanahan said she had no immediate word on whether Mrs. Steffey would meet with the students in College Hall. College President Mary Maples Dunn met with them late Thursday, but Mrs. Shanahan said she did not know what was discussed.

''We will invite the help of students and faculty to set up an evaluation process of the companies which are doing business in South Africa,'' Mrs. Steffey said Thursday from her Pittsburgh home.

Mrs. Steffey said this was not an indication trustees had changed their minds and were leaning toward selling all stock in companies doing business in South Africa.

''I think the trustees right along have been very cognizant of the students' feelings and at the same time they have an important responsibility to address in terms of fiduciary obligations,'' she said.

At Brown, in Providence, R.I., the students said their water-only fast, which began at noon Thursday, was an ''act of personal revulsion'' against the college's investments. They said the fast could last more than two weeks.

But Dean of Students Eric Widmer said Thursday university officials would consider removing the students from Manning Chapel, despite sanctuary granted by a chaplain.

Widmer said the health risks of the fast ''obviously may invoke a higher principle than the principle of sanctuary.''

Leaders of the Brown Free South Africa Coalition listed demands, including that the university's governing body - Brown Corp. - vote by March 7 for immediate and total divestment of all South African-connected investments.

Brown Corp. voted Feb. 15 for a limited sale of the school's $35.2 million in stock with South African ties.

The Smith students began the sit-in in College Hall on Monday and then linked arms and blocked doorways, preventing school officials from entering the building starting Tuesday.

The trustees voted Saturday to sell stock in two companies which had not signed the Sullivan Principles, which call for U.S. businesses operating in South Africa to abolish racial discrimination in the workplace. But that was reduced to one company after the school learned one had signed the Sullivan Principles.

The trustees also agreed to divest by June 1987 from companies which have signed but not followed the Sullivan Principles. The school has nearly $22.3 million invested in 25 companies with South African ties out of the school's endowment of $232 million.