Sen. Alan Cranston (D-Calif.), his campaign $355,000 in debt, yesterday announced a drastically revised plan for financing his bid for the Democratic presidential nomination, while his campaign manager predicted that Cranston would force former vice president Walter F. Mondale out of the race by the end of March.

"We feel we have this down to a three-way race now," campaign manager Sergio Bendixen said. "We will spend the next nine months making it a two-man race."

In an unusual news conference here, Bendixen unveiled a $5 million, 30-state strategy that he said would enable Cranston to knock Mondale out of the race quickly and then demolish Sen. John Glenn (D-Ohio).

The strategy calls for Cranston to redirect fund-raising efforts at small contributors because he has been unable to establish himself as a credible contender in the eyes of major donors.

"We just aren't able to attract the $1,000 contributors to our campaign," he said, adding moments later, "We're not going to get any of the smart money."

The Cranston campaign has long claimed that its candidate is one of the nation's best political fund-raisers, and Cranston has boasted that he is not afraid to ask for a buck.

"At the beginning of the campaign, we thought Alan Cranston could raise money easily," Bendixen said. "We found that wasn't the case."

Reports filed with the Federal Election Commission this week showed that Cranston raised $1.1 million during the last six months and was more in debt than any of the other five announced candidates. The reports also indicated that Mondale, who reported taking in $5.2 million, had raised about $600,000 in California, which is more than Cranston did.

Cranston's new financial plan calls for raising $2.2 million from direct mail by the end of the year, $1 million from television advertisments, $500,000 from rock concerts and $1.5 million from traditional fund-raising dinners and receptions.

Even if the plan succeeds, aides projected that Cranston would be $1 million in debt by Jan. 1, when he would become eligible for federal matching campaign funds.

FEC reports also show that Sen. Gary Hart (D-Colo.) is $224,896 in debt, and campaign staff members have said that he is negotiating for $350,000 in loans.

Cranston raised $3.1 million for his 1980 Senate campaign, more than any other Senate candidate. Last year, he raised $2.9 million for other candidates.

"I tell you Alan Cranston is still the best fund-raiser who has ever been elected to office in this country," said Mickey Kantor, who managed Cranston's 1974 Senate campaign. "If he were to run again for the Senate, he'd have no trouble raising great sums of money."

In addition, as a presidential candidate, Cranston has performed far better than expected, finishing surprisingly well in straw ballots at Democratic functions, using the nuclear-freeze issue to attract support.

Cranston aides had said they thought that a straw-poll victory last month in Wisconsin would give the campaign a major boost among big givers, but it did not. "Californians have a realistic view of straw polls," said Kantor, who now works for Mondale. "It's only the press that thinks they are important."

"You can't raise money from the nuclear-freeze movement," a highly placed Mondale aide said. "They're willing to stand up and be counted, but they don't give money to candidates."

Cranston aides, however, maintain that his straw-poll showings and support of the nuclear freeze have attracted thousands of small contributors. Bendixen said Cranston was receiving $3 for every $1 spent on direct-mail appeals to such donors and will have 70,000 to 80,000 contributors by March 31.

The centerpiece in Cranston's direct-mail campaign is a starkly worded letter that begins: "The Reagan administration's strategy is to win a nuclear war. My strategy is to ban nuclear war. The choice is yours."