After eight years of lectures about Spaceship Earth, vacation trips with rock stars and presidential manuevering, the governorship of California seems headed for quieter times, if everyone can stay awake through this year's campaign.

While the governor and media circus ringmaster, Edmund G. (Jerry) Brown Jr., goes off to run for the Senate, two of the most prominent, cautious and colorless politicians in the state are their parties' most likely choices to be his successor.

This has prompted one observer to make the dire prediction that California voters may suffer through a campaign waged on issues rather than personalities.

The two are Democrat Thomas Bradley, 64, mayor of Los Angeles, and Republican George Deukmejian, 53, state attorney general, both apparently dedicated to the proposition that strong, quick opinions lose elections.

A sampling of their campaign rhetoric suggests that political junkies in the nation's largest state may have to readjust to life in the slow lane.

Bradley was asked during a recent interview what he as governor would do about the $2 billion deficit the state is facing in the wake of federal budget cuts.

"It is very speculative at this time. You cannot talk about any sensible numbers, and for that reason I've stayed away from discussing the budget in any detail," he said. "I haven't looked at the federal budget or even the state budget, since that's not my responsibility."

Deukmejian was asked at a luncheon in Huntington Park if he favored freeing school construction funds to relieve overcrowding in the local schools. "I really haven't been that acquainted with it. It is not in the area of our jurisdiction," he said. "I don't think I should be knowledgeable about every local issue in the state."

While other Democrats rush to suggest alternatives to President Reagan's economic program, Bradley hangs back. "Until the president's program has clearly failed, who's going to listen to some new idea or new program . . . ?" he asked.

While other Republicans launch a drive to recall California Supreme Court Chief Justice Rose Bird, a Brown appointee, Deukmejian, no fan of Bird, also hangs back. He said he wants to see what form opposition to Bird and other Brown judicial appointees on the ballot takes.

Despite, or perhaps because of, their caution, the two have been rewarded with high standings in the polls.

The most recent California Poll shows Bradley as the choice of 58 percent of the Democrats, compared with 15 percent for state Controller Ken Cory, who withdrew last week, 6 percent for state Sen. John Garamendi and 5 percent for former state secretary of health and welfare Mario Obledo.

Deukmejian, who once trailed Lt. Gov. Mike Curb for the GOP nomination, now leads among Republican respondents by 43 percent to 32 percent.

A sample of all voters showed 50 percent for Bradley and 39 percent for Deukmejian, a substantial reduction of Bradley's 54 to 33 percent lead in the previous poll.

"It is difficult to imagine two duller candidates facing off in this era of smoke-and-mirrors politics," wrote Ed Salzman of the California Journal. He predicted, with some foreboding, a general election waged on issues rather than personalities, unfamiliar territory for Californians.

About the only bit of drama in this battle of political milquetoasts is the prospect of Bradley's becoming the first black elected governor in history. Even his race, however, does not seem to figure in the campaign.

"Polls that have been done clearly indicate that race will be an insignificant factor," Bradley said.

Bradley and Deukmejian are the oldest and most politically experienced candidates in their respective primaries.

Bradley, tall and reserved, is a sharecropper's son who became a star track athlete at UCLA, a policeman, a lawyer, a City Council member and thrice-elected mayor.

Deukmejian, a lawyer of Armenian descent, spent 16 years in the legislature before being elected attorney general in 1978.

Both are being attacked for their support of one of the most volatile issues in the state: the Peripheral Canal, a proposed 43-mile channel to bring more northern California water into the aqueduct serving southern California. A referendum on the canal will be in the June primary balloting.

Garamendi, 36, the senate Democratic leader, expressed the feeling of his fellow northern Californians in calling the project "wasteful and unnecessary." Curb, although a southern Californian, appears to have decided that support for the project in the populous south is broad but shallow.

"The bottom line is when the facts get out and the people start finding out that this is going to cost $10 billion at some point," Curb said in a television interview. "Then they're going to be pretty darn thankful there was one candidate who stood up and said, 'Let's look for an alternative.' "

Obledo's hopes depend on whether the 20 percent of the state's population of Hispanic origin will vote in large enough numbers to give him a viable base.

He scores Bradley for "moving toward the right," his close ties to city business leaders and his unwillingness to attack Reagan.

Curb usually attacks Deukmejian from the right. He points out that the attorney general did not support Proposition 13, the landmark tax-cutting initiative, and has shied away from the campaign to unseat Chief Justice Bird.

Curb looks younger than his age, 37, and has suffered from Deukmejian's references to his lack of experience. Until his election in 1978 he was a millionaire record producer who had never held public office.

He has retaliated with television spots that feature such luminaries as Rep. Jack Kemp (R-N.Y.), Ed Davis, former Los Angeles police chief and current state senator, former Los Angeles County sheriff Peter Pitchess and TV star Efrem Zimbalist Jr., extolling his experience and devotion to Republican principles.

He also hired Lyn Nofziger, Reagan's former political adviser, as a campaign consultant, and he has by far the largest bank account, about $2.2 million, compared with $1.3 million for Deukmejian. Bradley reports $713,579 in the bank, Obledo $15,549, and Garamendi reports a deficit of $53,057.

As the economy has worsened Curb and Deukmejian have curtailed their glowing references to Reagan and have focused their attack on Brown, particularly his judicial appointments.

Deukmejian regularly cites a study of state supreme court decisions which, he says, shows that a majority of the court "came down on the side of the criminal defendant 75 to 100 percent of the time."

Bradley usually refrains from discussing the Brown administration at all, but he said the attack on judicial appointments "is just distortion."

Bradley likes to relate that he is told that Deukmejian has confessed privately that no Republican candidate could match Bradley's "on-line experience in law enforcement," a statement about which Deukmejian aides deny any knowledge.

Tony Cimarusti, Deukmejian's press secretary, acknowledges that his boss is no spellbinder in front of audiences, and he anticipates more low-key debates on the justice system.

But after hearing Bradley address a recent gathering, Cimarusti said he felt better: "He makes George sound like a scintillating speaker."