"There are periods of bisexual chic," said Marjorie Garber, a professor of English at Harvard University and the author of a book on bisexuality in fiction and in society, "Vice Versa" (Simon & Schuster, 1995). "We're in a moment when it's visible again."

One reason is AIDS. A decade ago, the term "bisexual" suddenly came into much broader use because of concerns that bisexuals would be a conduit for the spread of AIDS to heterosexuals. Some bisexuals who felt they were being made scapegoats turned to political organizing. They formed groups like Bi Net USA, a coalition that has sought to win acceptance by gay rights advocates, who have not always welcomed them personally or as allies.

There have been battles to include the word "bisexual" in the names of gay groups. The issue dominated several raucous meetings last year of the committee that stages San Francisco's gay pride parade. This year's committee has adopted the name San Francisco Lesbian, Gay, Bisexual, Transgender Pride Celebration Committee.

"Bisexuals have had many experiences where they are explicitly not welcome in the gay and lesbian community," said Gretchen Lee, who advocated the name change. "If I come out to a lesbian woman as bi, I'll hear her say, 'A bisexual once dumped me for a man.' "

Robert Bray, an official of the National Gay and Lesbian Task Force, acknowledged that the gay rights movement had historically shunned bisexuals. "I've heard one gay activist say, 'What do they bring to the table?' " Mr. Bray said. " 'Their oppression comes from their homosexuality, not their heterosexuality.' " But he said that suspicion was lifting, particularly since bisexuals had been grouped with gay men and lesbians in initiatives against gay rights in Colorado and elsewhere. The Numbers Vary the Question, Change the Data

Bisexuals say they are stereotyped equally by homosexuals and heterosexuals. They are seen either as straight people who are indulging a taste for exoticism or as homosexuals without the courage to admit it. But an increasing number of scholars and bisexuals insist that this denial is ignorance.

"To me, I never felt like I had a stronger attraction to men or women," said Brad Dent, a clinical social worker in Fayetteville, N.C. In college, he said, he fell in love with a young woman and nearly married; then he had an intimate relationship with his male roommate for three years. "I didn't have a problem identifying myself as gay," said Mr. Dent, who is 29. "But I knew that wasn't the total picture."