LISA LEFF | Associated Press

SAN FRANCISCO — For the last 13 years, Lindasusan Ulrich has been in a committed relationship with the same woman. The couple have married three times, twice before it was legal in California and once while it briefly was. But if acquaintances were to assume Ulrich and her wife, Emily Drennen, are lesbians, they would be wrong. They identify as bisexuals and are proud of it.

This doesn’t mean their sexual orientation hasn’t presented challenges. Even in a do-as-you-like city such as San Francisco, the women have found bisexuals to be a misunderstood and often overlooked minority. During the state’s 2008 campaign to ban same-sex marriages, they forcefully reminded gay rights leaders — in the form of a cake decorated with the words “Having Our Cake and Eating It Too! Bisexuals Exist!” — that political advertising and fundraising appeals referring only to gay and lesbian couples did not encompass their imperiled union.

“It’s a unique identity as opposed to half one and half the other,” said Ulrich, a 41-year-old writer and musician who recently authored a report on “bisexual invisibility” for the San Francisco Human Rights Commission.

The commission unanimously adopted the report, and that could prove a significant step, said Denise Penn, director of the American Institute of Bisexuality.

Because San Francisco takes its commitment to gay and lesbian rights so seriously, shining a spotlight on the hostility bisexuals sometimes encounter from gay men and lesbians could help ease one of the most painful aspects of having a bisexual identity, Penn said.

“People don’t trust bisexuals, and I’ve heard some really, really nasty stuff,” Penn said. ” ‘Oh, you are going to just go back and hide in your straight world.’ Bisexuals are (seen as) tourists in the community, opportunists.”

As gay, lesbian and transgender people have succeeded in putting their fight for equality front and center in American politics, bisexuals — the often forgotten “B” in the LGBT rainbow — have been waging their own fight for recognition. From adopting a bisexual pride flag and commemorating Sept. 23 as bisexual pride day to urging researchers and government agencies to treat bisexuality as a distinct category, activists who acknowledge their attractions to both men and women say they want to assert their existence.

In promoting their not-insignificant ranks, activists point out that a UCLA demographer estimated last month that slightly more Americans self-identify as bisexual than as gay or lesbian. But the activist argue their task is complicated by stereotypes of bisexuals as fickle sex fiends, the difficulty in pinning down who counts as bisexual, and discrimination from both the straight and gay communities.

“Even people who would not feel comfortable saying bad things about gay or lesbian people still feel comfortable trashing bi people,” said Robyn Ochs, a veteran bisexual activist in Boston.

Johnny Fesenko, 42, a computer programmer in San Francisco, said that contrary to popular belief and jokes about male fantasies involving threesomes, living as a bisexual can sometimes feel like the worst of all worlds instead of the best of both. Gay friends and potential partners tell him his interest in women is just a phase. He’s had straight women refuse to date him because he’s not “a real man.” He once was punched in the face while walking with a boyfriend in Manhattan, he said.

“It’s almost like being called an atheist — you would rather call yourself agnostic because there is such a stigma associated with it,” Fesenko said.

Despite the inherent obstacles, activists point to signs of progress. The National Gay and Lesbian Task Force, one of the nation’s largest gay rights groups, a few years ago started holding bisexual-specific meetings and panels. Students at Ohio State University, the University of Michigan, the University of Minnesota have established groups for bisexuals. Out & Equal, a San Francisco-based organization that advocates for workplace rights for gays, last year sponsored an international survey aimed at uncovering on-the-job issues that bisexuals face.

“People really believe that bisexuality is covered by either gay issues or straight issues, so… you don’t need to worry about the whole middle thing,” said Heidi Green, a diversity trainer who co-conducted the survey. “Yet there are huge issues for bisexuals. When I ask people if they are out at work, the answer is almost universally ‘no.’ And because we don’t have really strong community, there is a tendency to believe the issues you have in your life are unique to you, there is something wrong with you.”

Chicago resident Adrienne Williams, a web content producer, launched the online Bisexual Social Network in late 2008 to fill what she considered a shameful absence of bisexual celebrities and entertainment in gay media. She still likes playing watchdog. One of her recent pet peeves is that gay publications celebrated the coming out of singer Ricky Martin, who was long rumored to be gay, but gave short shrift to Anna Paquin’s announcement, while she was engaged to a man, that she is bisexual.

Kate Kendall, executive director of the National Center for Lesbian Rights, acknowledges that gay and lesbian leaders have not always made their bisexual comrades feel appreciated. Within the LGBT movement, bridging internal divisions of race, class, gender and sexual orientation can take a back seat to combating bias on the outside, she said.

“What the movement must always be doing is looking around for whose issues are being ignored, whose issues are being left behind, who is not with us as we see gains being made,” Kendall said. “Certainly bisexual folks have a legitimate beef when they say that they have felt by turns disrespected and by turns ignored.”

Kendall’s advocacy organization last year sued the North American Gay Amateur Athletic Association on behalf of three bisexual men disqualified from playing in the 2008 Gay Softball World Series in Seattle. Their team’s eligibility had been challenged based on a rule limiting each squad to including no more than two straight players. During a hearing, the three players were asked whether they were predominantly attracted to men or women and other questions about their sexual orientations. A panel then voted on whether they were “gay” or “non-gay,” according to the still pending complaint.

“I thought we were going to get more resistance from lesbian and gay folks in the community, not only for representing these men, but suing a gay softball association,” Kendall said. “With a few exceptions, we have had overwhelming support, which I take as an indication that we as a movement overall have matured on this issue.”