The raucous family quarrel known as the 1986 California Republican senatorial primary has only a few hours to go. As in many large families, even quiet little brothers may sometimes come up with mischief to get attention.

So when an aide gave usually taciturn Los Angeles County Supervisor Mike Antonovich a plain paper bag during a commercial at a televised candidate debate this week, everyone became very curious. The instant the camera turned to Antonovich, he pulled out a milk carton adorned, like a photo of a missing child, with a picture of Rep. Edwin V.W. Zschau, the "Missing Candidate."

The other contenders laughed and applauded with glee. It is open season on Zschau (the z is silent), the congressman from the Silicon Valley who once founded a successful computer firm. Zschau has moved into the lead in recent polls by spending $2.4 million and avoiding many candidate forums where he might have defend his relatively liberal voting record.

The darts thrown in these family squabbles have been precisely aimed, but often rubber tipped. Except for one brief, bizarre criminal proceeding at the beginning of the campaign, the discussion has focused almost exclusively on legislative issues: federal budget limits, abortion, immigration, U.S. policy toward Central America and the Soviet Union. All contenders have said they are willing to help the victor beat still-favored Sen. Alan Cranston (D) in the general election.

Some hurts, of course, cannot be forgotten. Rep. Bobbi Fiedler pointedly changed her seat at the beginning of a 10-candidate debate this week so she would not be next to state Sen. Ed Davis. Fiedler and her chief aide Paul Clarke, who is also her fiance, were indicted five months ago when Davis accused them of trying to buy him out of the race with a $100,000 campaign contribution. The charges were soon thrown out of court. Instead, long-shot candidate and former Black Panther leader Eldridge Cleaver, a born-again conservative Republican, sat between the two adversaries and chatted amiably with Davis, a former Los Angeles police chief.

When tweaking Zschau loses its thrill, some contenders have done their best to chip away at the popularity of the other front-runner, former documentary producer and television commentator Bruce Herschensohn. The former aide to President Richard M. Nixon has been unable to match Zschau as a fund-raiser, but he is so well known in southern California from his years on the top-rated KABC news program that it has not mattered until now.

At the candidates' debate, Antonovich launched an assault on Herschensohn's flat-tax scheme, the target of a new series of television commercials designed by Antonovich's staff to whittle down his leading southern California rival. The flat tax, Antonovich said, would eliminate popular deductions for health care and mortgage interest.

Herschensohn bristled, and fixed on the camera -- rather than Antonovich -- with the forthright stare that has energized his own simple, issue-oriented commercials. "Mike. Mike Antonovich," he said. "The depth of your understanding of my issues is commensurate with the depth of a single piece of Saran Wrap."

A new survey by independent pollster Steve Teichner puts the two apparent front-runners much closer than the poll's 4 percent margin of error: Zschau 15 percent, Herschensohn 14 percent, Antonovich 8 percent, Fiedler 6 percent, Davis 4 percent, Assemblyman Robert Naylor 2 percent and economist Arthur Laffer 1 percent. (A private poll done for Zschau's campaign gives him 25 percent and Herschensohn 19 percent.)

Teichner's survey reported a 49 percent undecided rate, a number that gives hope to many contenders like Fiedler. "The polls elected Tom Bradley governor and Jerry Brown senator," she said, referring to two Democrats who lost in 1982 despite Election Day predictions of victory.

The crowded field -- 12 active candidates at last count -- opens the way, under conventional California political wisdom, for a possible Zschau victory. He was a little-known northern Californian who needed a divisive struggle among the major Los Angeles candidates -- Herschensohn, Antonovich, Fiedler and Davis -- to give him a chance by splitting the huge southern California vote. There will be no runoff.

His commercials are plentiful and slick. His campaign style, if a little unorthodox (he often sings at rallies), pleases audiences. He has received high ratings from reporters and fellow members of Congress, and his relative youth, 46, contrasts with Cranston, 71.

Herschensohn, with endorsements from Nixon, tax slasher Howard Jarvis and many strong California conservatives, gently shrugs off questions about Zschau's spurt and lets his tenacious pro-Americanisms speak for him. His commercials call for action against any terrorists who "hurt one hair on any American head or damage one blade of grass on any American property." He would sign no agreements with the Soviets that involved American concessions and would oppose the Gramm-Rudman-Hollings antideficit law because it threatens a U.S. arms buildup to achieve superiority over the Soviets.

Antonovich supports a more conventional Republican agenda, buttressed by his ballyhooed support for U.S. troops to stop illegal immigrants from crossing the Mexican border.

Back at the tail end of the pack are less well-known candidates. Cleaver is joined by former Oakland Tribune publisher Joseph Knowland, Los Angeles attorney George Montgomery, oceanographer John W. Spring, and psychologist William Pemberton.