During a difficult winter of deepening national recession, Republican candidates for California governor did not mention their favorite president. But springtime brings the usual hopes, and Republican politics has returned to its favorite theme: who is closest to Ronald Reagan?

Under the hot television lights of their last joint appearance before the June 8 primary, Lt. Gov. Mike Curb, 37, and attorney general George Deukmejian, 53--who both wish to become the first Republican governor here since Reagan--ignored their few other differences to argue bitterly over who was most loyal to the president.

It is an important question, for after spending millions of dollars on mailings and television advertising, these two men so different in age, temperament and experience find they must both pass the same Reagan litmus test to have a hope of winning the state's unabashedly conservative Republican voters.

But it puts them in a classic Republican political bind, for the test narrows the base from which one or the other must attack this season's colossus of California politics--Tom Bradley, the enormously popular mayor of Los Angeles. Bradley is far ahead in the Democratic primary and leads both Curb and Deukmejian by 26 percentage points in trial-heat polls.

Deukmejian, behind at the beginning of the campaign, profited from Curb's outbursts of temper at press conferences and led the youthful lieutenant governor, a millionaire former record producer, by 11 percentage points in February.

A veteran of 16 years in the state legislature and four years as attorney general, Deukmejian followed the cautious course which had worked so well for Bradley. He answered questions only in a general way and avoided controversial stands.

But Bradley had to satisfy a wide spectrum of opinion among Democrats, while Deukmejian had to appeal to mostly conservative Republicans. Suddenly, Curb's sharper and consistently conservative stance on issues has brought him back to a 50-to-35-percent lead over Deukmejian in the latest Los Angeles Times poll.

At the taping of KNXT-TV's Newsmakers show, the cautious, lawyerly Deukmejian finally exploded in calculated indignation at Curb's efforts to label him disloyal for failing to take a stand in Reagan's 1976 presidential primary contest with President Ford. With the help of a reporter, the Deukmejian campaign had discovered that Curb had not been registered to vote until 1974, after Reagan's two gubernatorial campaigns.

"While I was working side by side with Gov. Reagan in the state legislature, Mike Curb didn't even care enough to register to vote," Deukmejian said.

Curb, apparently unaccustomed to being on the defensive, backtracked feebly: He said he had to travel a great deal as a record producer and "the fact that I registered in 1974--I was still in my 20s at the time--I think that was a proper thing for me to do. It might have been better if I'd registered earlier."

Deukmejian said his campaign may use the issue of Curb's tardy registration in its television advertising. "When things get tough, the tough have to fight harder and work harder," he said. But an exchange during the joint television interview on the welfare issue indicated how much faster Curb still is in getting to the heart of issues that enrage Republicans.

Deukmejian: "I think that we need to do everything we can to encourage welfare recipients to work and to make it possible for them to work. . . ."

Interviewer: "You agree with Mr. Curb in saying that it's too easy for people not to work and still get along, therefore they don't take these jobs that these people come in from other countries to take?"

Deukmejian: "I think there is no question that there are many cases like that. I do feel that the overwhelming majority of people would like to work. I do feel that they would like to be self-supporting. I don't feel that the majority of the people are just lazy and want to live off the public welfare. . . ."

Interviewer: "Mr. Curb, are you implying that there are a lot of people who are just lazy, if they can get by, they get by?"

Curb: "I sure am, and this is a major issue where the two of us disagree."

Deukmejian discounted Curb's lead in the polls. He pointed out that he appeared to be trailing his Democratic opponent in the 1978 attorney general race before he won a sizable victory.

But Curb and his campaign manager, Ken Reitz, have been unusually adept at picking issues that put Deukmejian on the defensive.

In a gamble that first puzzled many veteran politicians here, Curb decided late last year to oppose the Peripheral Canal, then a popular project to bring more water to southern California. Deukmejian continued to support the project, and chided Curb for changing from his initial support.

But an expensive anti-canal television campaign has underlined the project's enormous costs to consumers, and now opinion has turned around, with 52 percent of voters saying they oppose the canal.

Deukmejian also relinquished a natural advantage he had as attorney general on the anti-crime issue. He has let Curb lead the assault against the pro-defendant decisions of state Supreme Court Chief Justice Rose Bird, thought by many California Republicans to be the most disagreeable appointment Democratic Gov. Edmund G. (Jerry) Brown Jr. ever made. Cautious as ever, Deukmejian has argued that a campaign to recall Bird--which Curb supports--is a waste of Republican resources and should be reserved for cases of judicial malfeasance, corruption or moral turpitude.

When it appeared that Deukmejian would be the Republican nominee against Bradley, political columnists here began to look toward a somewhat cautious and lackluster general election campaign. Bradley continues to take few chances--he has yet to say what he thinks of the controversial, anti-crime "victims bill of rights" on the June 8 ballot.

Curb, anticipating a victory over Deukmejian, seems to be enthralled with the prospect of another cautious opponent.

"I'm tired of talking about other Republicans," he told a women's group recently. "What I want to do is talk about Tom Bradley as much as possible."