Stanford University has adopted what may be the nation's broadest policy on college housing, providing it and other benefits to unmarried couples, including homosexuals, who are involved in long-term relationships.

The new policy, announced Tuesday and in effect immediately, was reached in negotiations initiated by a group of gay graduate students in May 1989. The students argued that granting unmarried couples the same benefits as married ones was consistent with Stanford's pledge not to discriminate on the basis of sexual orientation.

Unmarried and gay couples will be eligible to rent subsidized apartments in high-rises on the campus near Palo Alto, Calif.

Non-student "domestic partners" of Stanford students also will have access to university libraries, athletic facilities and campus events usually open only to students, staff and faculty members. The partners will also be able to purchase medical care at a campus health center.

Previously, Stanford extended such benefits on a case-by-case basis. Norm Robinson, acting dean of student affairs, said the university wanted to "ensure that students do not have to choose between their domestic commitments and their studies."

The new policy defines a long-term relationship as involving couples who have "a mutual commitment similar to that of marriage. . . and share the necessities of life and responsibility for their common welfare."

Ivy Young, director of the Families Project of the National Gay and Lesbian Task Force, said Stanford's policy is the probably the broadest of any college's in the country.

She named eight other schools -- ranging from Harvard and University of California at Berkeley to the University of North Dakota and Miami University (Ohio) -- that have less extensive domestic-partner policies. "They primarily affect housing," she said.

Young, whose Washington-based organization is surveying colleges on the issue, said such policies "remove discrimination on how you construct families" and "recognize the diversity of campus life."

David Bradfute, 25, a doctoral candidate in biology, said the new policy would most affect graduate students who are older and more likely to have a long-term relationship.

In addition to the benefits, he said the change has "the deeper significance" of gay students "really being welcomed to Stanford for the first time."