A Kinsey report on homosexuals in San Francisco, quoted on a CBS documentary tonight, estimates that the average gay man in that city has had sexual relations with "at least 500 different men" and that 30 percent have had such encounters with more than 1,000. A gay activist is asked what such figures suggest.

"I don't think that it means moral decay," he replies, but this CBS Reports broadcast, "Gay Power, Gay Politics," at 10 on Channel 9, has a different attitude. It depicts a city whose officials cower under pressure from homosexual groups and where little children are exposed to sexual acts committed in public.

Not a pretty picture, no no no, and not an accurate one, either, according to some homosexual groups who have denounced the program in advance. Indeed, the report, produced by Grace Diekhaus and George Crile, seems unusually determined to shock and titillate, not always in a spirit of clearest relevance.

The disclaimer is right up front: "Gay power, gay politics, that's what this report's about. It's not a story about lifestyles or the average gay experience.c "But the impression many viewers will glean from the program is that homosexuals have taken over one American city, San Francisco, and are planning on laying seige to others.

"We shall be free, because we are everywhere," a lesbian shouts at a rally. America may take this as a threat. Shots taken at a Halloween celebration make it look as if it is the ambition of homosexuals to dress in feathers and kiss one another in front of children. Later the report cuts abruptly from a "respectable" gay banker to shots of outlandish leather paraphernalia used by the sadomasochistic homosexual fringe.

The topic is still so inflammatory that there many be no way to present it in a nonhysterical way on television. And some gay groups tend to protest any discussion of their "lifestyle" that doesn't amount to a recruitment film. But "Gay Power, Gay Politics" appears to use sensational footage at regular intervals to keep viewers interested and, perhaps unjustifiably, alarmed.

Although correspondent Harry Reasoner gets star billing, producer-reporter Crile did all the work for this report. Reasoner's smirky and laconic presence is confined to the opening and close. And although the program is flawed and ill-focused, Crile comes across as a diligent and intelligent TV journalist. May he go from this frying pan into a more manegeable fire.