"Someone in your life is gay," says the ad as photographs of Washington-area homosexuals, including three couples, look out at you.

The ad was drafted by the local Gay Activist Alliance to be used in subways and buses. But Metro officials rejected the ad, citing a guideline adopted by the Metro board last month on controversial advertising.

And so yesterday the alliance, a group of homosexuals organized to promote the welfare of gays locally, called a news conference in front of Metro's downtown headquarters to announce that a $10 million lawsuit was being filed against Metro charging the agency with violating the District's antidiscrimination law.

The purpose of the poster ad is to educate the public, said alliance president Bob Davis. "When they talk about gay people they are talking about people they know. Respectable hard-working people." Homosexuals "are not freaks," he said.

Metro general manager Theodore Lutz said his staff based its rejection of the ad on guideline adopted by the Metro board last month dealing with controversial advertising. The ad was received last spring and the gay alliance was notified that the ad was rejected earlier this month.

The new guidelines say in part: "Items which might be objectionable to a substantial segment of the community should be avoided. For example, advertising depicting or referring to undesireable social behavior or which might be offensive because of racial or religious references should be avoided."

"The issue is, should our bus vehicles be a forum for these controversial community subjects," Lutz said, and "how much should the captive audience (bus and subway riders) be subjected to controversial issues."

Lee said the posters were "a subtle campaign in conscious-raising."

Advertising on Metro vehicles has become intensely popular since the subway started operating, said Metro spokesman Cody Pfanshiehl.

Buses and subway now carry ads for political candidates, cigarettes, whiskey, the Coast Guard and for antishoplifting campaigns, for example.

It was this popularity of subway advertising space.Pfanshiehl said, that led the Metro staff to ask the board to review advertising guidelines adopted six years ago.

The board, which consists primarily of local politicians voted on Sept. 21 to keep all 10 of the old guidelines, which generally call for all advertising to be truthful. Then, at the staff's recommendation, an 11th guideline was added to cover controversial topics, according to the minute of the meeting.