Washington — Walter Mondale has decided to make a fight of it this fall in President Reagan's home state of California. Maybe.
A month ago, politicians rated Mr. Mondale's prospects near zero in the Golden State, where Ronald Reagan has reigned supreme since he began an eight-year tenure as governor in 1967. Mr. Reagan has won every election in California by at least half a million votes. He whipped Jimmy Carter there by nearly 1.5 million.
Yet Mondale has hope. Something has changed, and that change is spelled F-E-R-R-A-R-O.
Geraldine A. Ferraro, the Mondale running mate for vice-president, has brought so much freshness and excitement to the Democratic ticket that Mondale aides say California could be winnable.
US Rep. Tony Coelho (D) of California reports that Mondale will send one of his top deputies, campaign manager Robert Beckel, out to the West Coast this week. The candidates are expected to follow soon afterward.
Mr. Coelho says polls in California show ''tremendous movement'' since Mondale picked Ms. Ferraro. All of a sudden, ''Ferraro is catching on'' there. The situation is ''hot,'' Coelho told reporters at a breakfast meeting here.
Mr. Beckel will be telling California party leaders that Mondale has decided to battle for the state to ''make it competitive'' in November.
In the last few elections, Democratic presidential nominees have quickly written off California - and that has been a mistake, Coelho says. California elections turn on ''personalities,'' not parties or ideology, he insists. And this means that the addition of Ferraro, an outspoken, colorful congresswoman from Queens, could make the Democratic campaign there take off as fast as a Steven Spielberg movie.
Optimism is growing in the Mondale campaign, even though news in the past few days has been mixed. On the downside: a national poll that shows Reagan pulling far ahead once again, Bert Lance's resignation from his new post as general chairman of the Mondale campaign, and a roaring Wall Street market that could send Reagan's stock even higher.
The national poll results were expected. Two weeks ago, just as the Democratic convention ended, a Gallup poll taken for Newsweek put Mondale-Ferraro two points ahead of Reagan-Bush. But today the Reagan team is once again out front, this time by 10 points, Gallup reports. The GOP convention that begins Aug. 20 in Dallas should give another upward push to the Republicans.
The story about Georgia banker Bert Lance was Page 1 news all over again, just as it had been last month when Mondale picked him for a top position in his campaign. Party insiders were relieved to see Mr. Lance go. They said he carried too much ''political baggage'' - he had been forced out of the Carter White House seven years ago by an investigation of his banking practices - and all that unhappy history was dredged up again when Mondale selected him. The Lance news took a little of the luster off the Mondale-Ferraro team's first week of campaigning together.
By election day, however, Lance's resignation will probably be only a distant memory, like the summer Olympics and the All-Star baseball game.
''It's one of those little blips on the screen which by November will be of little import,'' says a political analyst in South Carolina. Its main impact now is to remind voters of the Democrats' difficulties in Dixie.
A Southern party insider on Capitol Hill says that, as of today, Reagan would probably carry every Southern state.
The stock market surge, of course, isn't something Mondale can do anything about.
The market's sensational rise last week could be a signal that Mondale is about to lose one of his prime issues: rising interest rates. The good stock market stemmed in part from a belief that interest rates have peaked.
Other economic news, however, played neatly into Mondale's hands. His major domestic issue is ''fairness'' - his charge that Reagan is tilting government against the poor.
At week's end, new official figures showed that the jobless rate had suddenly risen during the past month (reversing a long-term trend), and that the number of Americans living in poverty had gone up in 1983.
Encouraged by the latest campaign outlook, Democratic Party political director Ann Lewis now calls the election ''up for grabs.''
She looks for a Mondale breakthrough in former Reagan states like Ohio, Illinois, Texas, Missouri, and Mississippi.