Ronald Reagan demonstrated his home-state political muscle today when his supporters on the Republican State Central Committee crushed a proposal to do away with California's winner-take-all presidential primary.

The proposal, initiated by a supporter of GOP presidential candidate John Connally and backed by a coalition that ranged from the far right to the left of the Republican Party, was defeated by slightly more than 3 to 1. The victory gave Reagan, an undeclared candidate for president, an apparent hammerlock on California's 168 delegate votes at the 1980 Republican National Convention.

"We were trying to iron out our differences," quipped proportional representation sponsor John G. Schmitz after the vote. I was the ironee."

The vote today technically was an advisory one to the legislature on a bill by State Sen. Schmitz that would have made the 1980 primary proportional if no candidate received 50 percent of the vote. But in accordance with long custom, the legislature had indicated that it would abide by the central committee's decision.

The California block of delegates is the largest of any state and the winner-take-all system, last in the nation, gives the state GOP delegation distorted strength in the national convention where 997 votes are needed for nomination.

Reagan wants to keep it that way. Mocking the "let's be fair" slogan of those favoring proportional representation, Reagan's backers said that the Schmitz bill was simply an attempt to undermine the former California governor's coming presidential campaign.

"Ronald Reagan is our favorite son," said state Senate GOP leader William Campbell, a leading Reaganite. "Winner-take-all is good for us. It's good for party unity."

Recent surveys by California public opinion pollster Mervin Field show that Reagan is the overwhelming choice of COP voters but that 64 percent of them also favor a proportional system.

Recognizing this, a group of moderate Republicans led by Fresno County GOP chairman Richard C. Crossman announced immediately after today's vote that they would attempt to qualify a proportional representation initiative on the June 1980 ballot. But it is unclear whether the proposed initiative, which raises other issues as well, would apply to next year's presidential primary.

Despite losing by a bigger-than-expected margin today, the sponsors of the Schmitz bill assembled the broadest coalition ever seen at a California state GOP gathering.

Supporters of proportional representation ranged from Schmitz, a self-styled "born-again Republican" who was the American Independent Party candidate for president in 1972, to Rep. Paul N. (Pete) McCloskey (R-Calif.) a GOP liberal who opposed Richard Nixon that year on the Vietnam war issue.

Also among the supporters were former representative Charles C. Wiggins, once a staunch Nixon defender, and David Eisenhower, Nixon's son-in-law. Eisenhower, who was greeted with warm applause, argued that the GOP should open itself to "controversial ideas" by changing the system.

The only argument that counted, however, was that winner-take-all benefits Reagan's candidacy. Soon after the vote was taken, a straw vote of delegates showed Reagan the first presidential choice of 72 percent of those attending the convention, compared with 18 percent for Connelly.

The vote on the Schmitz proposal was similar -- 75.6 percent opposed and 24.4 percent in favor.

California winner-take-all primaries have loomed large in the nation's political history. Barry Goldwater assured himself of the GOP presidential nomination by beating Nelson Rockefeller here in 1964. And George McGovern clinched the 1972 Democratic nomination by defeating Hubert Humphrey in another close contest.

Since then, the Democrats have abandoned the winner-take-all system in all states.

The weekend GOP convention that concluded here today was, in effect, a Reagan rally. Since Reagan was the only candidate allowed to address the Saturday night banquet, all other GOP presidential candidates skipped the convention entirely.

Reagan used that banquet speech to outline his first specific opposition to the pending strategic arms limitation treaty.