More than 350 people were gathered at the plush, high-ceiling ballroom of the Sheraton Palace Hotel here one day last month to hear a speech by Mayor George Moscone.

The representives of more than 250 business were celebrating the fourth anniversary of the Golden Gate Business Association, a kind of chamber of commerce with a San Francisco twist.

All of the member businesses either are run by or cater to the rapidly growing homosexual community here.

The GGBA is another manifestation of the realization by the gay community of the power it weilds through its economic impact. The association encourages its members to do business with each other, to proctect themselves from sanctions by anti-gay businesses.

The city's political community is not unaware increasing clout of the gay community. Early in March the San Francisco board of supervisors tentively approved, by a voten of 10 to 1, a new gay rights law. It would outlaw discrimination "on the basis of sexualy orientation" in housing, jobs and the use of public accommondation.

"First of all, at least one quartet of the city (pop. 650,000) is gay," claims John schmidts, an insurance broker who heads the GGBA, "and the average gay is better educated, spends more money, and doesn't have the problems of a family man with all the accompanying responsibilities."

All of the member business either estimates of the number of homosexuals in San Francisco, few argue that it is a larger community. and most open of any in the nation.

In the past three years alone, the number of gay bars has more than double to over 200 in the five-county area around San Francisco. Estimates of the business done by gay bars in Calofornia last year along are in the $20 million range.

Most visible is the emergemce of neighborhood civic groups in areas where gay business predominates. The Castro Village Association, a gay-oriented business group, last year sponsored an all-day street fair that attracted more than 40,000 people.

Among the gay-owned or operated business on Castro Street that have opened in the past 18 months alone: Two barber shops, four men's clothing stores, one delicataseen, one restaurant and three gift and novelty shops.

While the Castro Street neighborhood had no openly homosexual businesses until the 1960s, it now typifies what is happening in many areas of this city. Firts, a few homosexual bars and bath houses opened, leading to a steady influx of business either run by, or catering to homosexuals.

On both Castro and Polk Streets here , homosexual gay-run small entertainments took over failing or shutered storefronts and bars and renovated them into a vanity of small businesses. Outside these neighborhoods there are other signs: gay-oriented resorts recreational areas like the Russian River, and both new and established real estate firmsd that have begun to cater to gay home buyers.

About half of the gay bars in the San Francisco area belong to the Tavern Guild, an association that is designated to protect and promote their interests. Money from the guild treasury, which he held as much as $100,000 at a time is used for vharitable donations and contribution to gay causes like the flight against Anita Bryant's campaign in Miami.

When the Tavern Guild last year thought that Coors beer officers had contributed to the Bryant crusade (although Coors issued a denial), a guils-member boycott of Coors contributed to the beer dropping from the number one sales slot in California.

Coors claimed, however, that the drop in sales actually was caused by an aggressive marketing campaign by its successor in the top position: Anheuser-Busch.

In addition to its growing economic clout the homosexual community also is experiencing increased pollitical strength here.

Harvey Milk, a veteran gay political activist, was elected to the city's Board of Supervisors last year, the first avowed homosexual to win election in a major U.S. city. He has seen to it that gay issues are hired before the city's ruling body.

Perhaps the best gauge of the growing importance of the gay community here is that the generaly business sector has begun a slow, but deliberate attempt to attract the gay consumer.