There is a minor mystery surrounding Walter F. Mondale's strategy in this first week of the general election campaign. Pundits and politicians are wondering: Why have Mr. Mondale and his running mate, Geraldine A. Ferraro, spent so much time in California?
Even the President Reagan's election officials are puzzled. Says Reagan-Bush spokesman John Buckley: ''It's a little hard to understand what Mondale is doing. It flies in the face of political logic.''
That may or may not be true, but Mondale strategist Tom Donelan concedes: ''We are pouring a lot into this state.'' Another aide says the Western swing reflects ''gut instinct'' that the region is ripe for a Democratic upset.
San Francisco pollster Mervin Field suggests Mr. Mondale and Ms. Ferraro may have been forced to make a fight for California - the President's home state - because the outlook is even less promising in other key states. He says:
''My feeling is that it's just a matter of how dismal the prospects are for Mondale in other areas. ... This state would have to be considered highly favored for Reagan.''
David Chagall, who publishes Inside Campaigning in Los Angeles, recalls that ''John Kennedy couldn't even carry California in 1960. There's little hope of Walter Mondale carrying it in 1984.''
So what is Mondale's plan? After launching the general election campaign with events in New York City and Merrill, Wis., he boarded a chartered plane and made a beeline for the West Coast. His running mate was with him. They landed in Long Beach, Calif., and immediately held a joint rally with leading local and national Democrats, such as Mayor Tom Bradley of Los Angeles, California Sen. Alan Cranston, former Gov. Edmund G. Brown Jr., and Sen. Gary Hart of Colorado.
The following day, Mondale visited a meatpacking plant, then flew to San Jose to meet with college students and educators, while Ferraro worked the San Diego area. Later their paths crossed again in Portland, Ore.
Despite the somber views of California experts for a Mondale victory there, his staff remains stubbornly upbeat - reflecting, according to press secretary Maxine Isaacs, Mondale's own conviction that he can ''win it.'' Ms. Isaacs says he is sure his chances are excellent in Oregon, Washington, and California.
Campaign aide Donelan says private polling shows Mondale is close enough to overtake Reagan's California lead. He also thinks Ferraro's name on the ticket will be a boost.
Focusing on the West, of course, has taken Mondale momentarily away from his own home base, the Midwest and Northeast. Isaacs says Mondale planners disagree with critics who say that in failing to ''secure'' his own base, by campaigning there first, he risks a terrible drubbing in November.
That's shortsighted, Isaacs says, and Mondale isn't going to ''fall into that political crack.'' At the moment, the campaign is admittedly behind in every region. That means, she says, that geography makes little difference - that Democrats must fight for votes everywhere.
Another aide says simply: ''California is the biggest state. Of course we're going to battle for it.'' Mondale cannot afford to limit his search for votes only to those areas where he is strongest, the aide insists. That would certainly be a recipe for defeat.
President Reagan, launching his own effort here in his home state, is obviously taking a different tack. His team wants to lock up his base - the West and the South. Then, assured that those areas are safe, he will turn full force toward battleground states in the Northeast and Midwest, especially New York, New Jersey, Pennsylvania, Ohio, Michigan, and Illinois.
Analysts Field and Chagall say there may be more than meets the eye in Mondale's foray into the West, especially into California.
The Golden State is perhaps the biggest source of money for the Democratic Party. And money is in short supply. It is desperately needed for voter registration and other party-building efforts - projects for which the GOP is spending millions.
Some California Democrats, however, would be unenthusiastic about writing checks with all those 000s at the end if Mondale & Co. failed to make an effort in their state.
Mr. Chagall labels the Mondale campaign's efforts in California ''an elaborate charade,'' conducted to mollify the big givers. Mr. Field makes a similar point: ''It's going to be tough for Mondale-Ferraro to get money out of California to use in other states unless he does something here.''
Experts say there could also be one more factor making California a tempting target. The state will vote in November on two reforms - reapportionment and campaign spending - issues that have concerned many Democratic regulars.
The reapportionment reform would take the job of determining the boundaries of state and federal districts out of the hands of politicians and put it under the control of a nonpartisan, blue-ribbon commission. That could threaten many officeholders, especially Democrats.
Another proposition would put strict controls on campaign contributions and spending. It could make significant changes in the state's election results.
Some Mondale supporters hope that California Democrats will get out the vote mainly to defeat these propositions.
The result could be a reverse-coattail effect, with the presidential ticket helped almost as an afterthought.
Mondale, of course, will take help like that anytime he can get it.