Four times in the last 20 years, Ronald Reagan's presence at the top of the California ballot has led the Republicans to large Election Day victories in this nation-state. But never again will Ronald Reagan's name appear on a ballot. So the June 3 primary to pick the GOP nominee to run against three-term Democratic Sen. Alan Cranston will provide the first clue as to the course the California GOP will take in the post-Reagan era.

With three weeks to go, the main options look to be these three disparate individuals:

The Yuppie Hero: Silicon Valley Rep. Ed Zschau, who, while the most popular professor at the Stanford Business School, became a millionaire by founding in his garage (where else?) a mini-computer storage disc company. Zschau's eclectic politics generally favor a minimum of governmental regulation of both personal behavior and economic activity.

The Right Stuff: Bruce Herschensohn, a onetime presidential speech-writer, who in the summer of 1974 fought loyally for and beside his leader at the political Dien Bien Phu that was then the Nixon White House. Herschensohn, even while unapologetically defending friendly right-wing dictators, is a terrific communicator.

The Unthreatening Arch-Conservative: The Prince Valium of California, Los Angeles county supervisor Mike Antonovich, whose constituency is bigger than the population of 42 states, may be short on charisma, but he is, as he is quick to recite, long on re'sume' ("1964 state youth steering committee for Barry Goldwater"). But in raising campaign funds, Antonovich is second only to Zschau, who has successfully wooed and won most of the state's business-political Big Money.

How important is money in California campaigns? Consider these items: It's a state with a larger population than East Germany or Canada and where one 30-second political commercial on prime-time (8 p.m. to 11 p.m.) on a single Los Angeles station can cost more than $18,000. That doesn't leave much time for block parties with Joe Sixpack. According to Zschau's campaign, since last July more than 90 of his scheduled campaign events have been "meet and greet big donors" meetings.

But is it worth all that GOP effort and energy to run against Cranston, a well-heeled incumbent? Probably. Cranston's positive rating is down to 37 percent this month in one statewide poll, from his high of 56 percent in 1981. Also, voters of any state are funny people; they are generally pleased when one of "their" officeholders is mentioned for national office, even when that officeholder runs for the nomination. But the voters' pride turns to displeasure when the home-state candidate, as most do, fails to win the White House. Ironically, Cranston could benefit from the total failure of his 1984 presidential bid. Because he wisely got out of that contest so quickly, Democrats are betting that in 1986 California voters will have forgotten Cranston's prematurely orange hair and ardently dovish platform.

Anything but dovish is Bruce Herschensohn, who, if there were a Political Truth-in-Packaging Award, would retire the trophy. A Los Angeles radio and TV commentator for the past eight years, Herschensohn may well be the only major statewide candidate in America this year without a research assistant or a speechwriter. His personal research is the basis for all the positions he takes and the speeches he makes. He writes all his own stuff, including his TV commercials, and what stuff it is. There are no birds or bunnies or beautiful sunsets in Herschensohn's TV spots: just the candidate, in his own nonmushy words, arguing for a flat tax of 16.4 percent with "no exemptions, no exclusions, no deductions," which would mean "no deficit"; or defending Pentagon spending: "Look, if we spend too much on defense, we're going to waste a lot of money. But if we spend too little on defense, we're going to waste the experiment called the United States of America." His message is the same at every forum, before every crowd.

The latest Field Poll, released Tuesday, showed Herschenson leading with 18 percent of the vote, Zschau tied with former Los Angeles Chief of Police Ed Davis at 15 percent, and Antonovich trailing with 8 percent. Nervous opponents have criticized Zschau's "liberalism" (anti-MX, pro-ERA), but that could backfire in a state where independence is a prized cultural value ("my own space") as well as a political value. It remains a race without a clear front-runner or an overriding issue. One leading California Republican puts it this way: California, with 11 peaks higher than 14,000 feet, "asks the Lord to send us men to match our mountains." In 1986, he says, "the Almighty thought we were Kansas."