Constituents have suspected him of bigamy. Callers have damned him for statements he never made. Hotel clerks have greeted his arrival with confused and disappointed looks.

It is not all cheers and confetti being Gary Hart, especially if you are not the same Gary Hart who last year became a household word and nearly won the Democratic presidential nomination.

Nevertheless, for a tall, handsome California state senator who happens to bear the same name as the tall, handsome U.S. senator from Colorado, the confusion has produced an unexpected bonus.

In the media-driven circus of late 20th-century American politics, having a familiar name is half the battle. What would otherwise be no more than an odd and amusing coincidence has turned a legislator described by one supporter as "not flashy," a man who has never run in any statewide election, into a contender for the California governorship.

"Usually a politician has to spend millions of dollars to acquire that kind of name identification," said Hart's chief of staff, Jerry Seedborg. Gary Warren Hart's national publicity and smashing victory in the 1984 California presidential primary made Gary Kersey Hart's name unforgettable and put him near the top of the list of candidates for the job held by Republican Gov. George Deukmejian.

When it was revealed that the Colorado senator had been born Gary Hartpence and changed his name, supporters of the Santa Barbara senator began to refer to him as "the real Gary Hart."

If the California Hart had no achievements to back up this public relations windfall, Republican tacticians would not be so concerned. But in eight years as an assemblyman and two as a state senator, Hart has steered politically potent education, environment and drunk-driving bills through the legislature.

By heeding his constituents' environmental concerns and standing up to the powerful California Teachers Association, Hart has kept liberals and conservatives happy. His district, which until recently included President Reagan's ranch, has a scant 47-to-41 percent Democratic registration advantage, but Hart, a self-confessed liberal with close ties to the West Los Angeles organization of Democratic Reps. Henry A. Waxman and Howard L. Berman, holds his own.

He stopped for an interview in this East San Francisco Bay community on a round of political stops to test his support for a governor's race. Los Angeles Mayor Tom Bradley and State Sen. John Garamendi, who have run statewide campaigns, are formidable potential opponents for the Democratic nomination. But Hart said frustrations of the Deukmejian years justify the risk, if he can find the money.

"Our greatness in the past has been due to governors who I think have some foresight into where California can and should be going, and I don't think this governor has that at all," he said. "I had my whole legislative program vetoed last year. The whole idea of six more years of waiting around for him to retire during the most productive years of my life is not very appealing."

Hart said he and his wife, Cary, a pediatrician, and their three young daughters are ready for a statewide campaign and the mixups that are sure to result -- some of them, inevitably, from Cary Hart's name. Hart staffers recall one constituent, thinking he was seeing the California senator on television, calling to ask "why Gary kept calling his wife Lee." That's the name of the Colorado senator's wife

Both Gary Harts were baptized politically in the antiwar movement and have been friends and occasional allies since. They first met in 1971 when the Colorado Hart came through California as presidential candidate George McGovern's campaign chairman.

While working toward a master's degree in teaching at the Harvard University Graduate School of Education, the 22-year-old Gary K. Hart was discovered by antiwar activist Allard K. Lowenstein. Hart worked in Eugene McCarthy's presidential campaign and then helped manage Lowenstein's winning 1968 race for a Long Island congressional seat.

He returned to Santa Barbara, taught high school history and social studies and plunged into local politics, becoming a master of door-to-door campaigns.

By the time Gary W. signed on as McGovern's chairman, Gary K. had managed one losing race for Congress and was known to political cognoscenti on both coasts. In those days, said Gary K., Gary W. "had a problem being confused with me."

In July 1972, with Gary W. in town snagging votes for McGovern and Gary K. running for the state assembly, the Santa Barbara News-Press published side-by-side photos of the two Harts. Both wore white shirts and wide striped ties, held telephones to their left ears and balanced notes on their laps while their pen-wielding right hands rested on stacks of mail. The only noticeable difference was Gary W.'s much longer hair, "and that might lose me votes in Santa Maria," the newspaper quoted Gary K. saying.

The catastrophic McGovern defeat at the hands of President Richard M. Nixon had much to do with Hart's 600-vote defeat in the 1972 assembly race. But he won two years later and moved to the state senate in 1982.

In that time, the Harts have done each other far more good than ill. Gary K. endorsed Gary W. for president in 1984, attracting many reporters looking for a bright way to start a story. It was one way of repaying Gary W. for his 1978 trip to California to headline a Gary K. fund-raiser, billed, as one might expect, the "Hart-to-Hart" Dinner.