When Gov. Edmund G. Brown Jr. appeared at a fundraiser here one week before California voters were about to approve huge property-tax reductions, he demonstrated an extraordinary political agility that may yet propel him into the White House.

Brown is an avowed opponent of the consitutional amendment (sponsored by anti-tax crusader Howard Jarvis) cutting $7 billion in property taxes, and so were most present at the posh Kona Kai Club who had spent $125 a plate. Nevertheless, there was no call to defeat Jarvis. Rather, Brown quietly called it "the latest manifestation of a very serious unease about government" and hoped his response to it could produce a "renewed charter" for government.

That climaxed a week of hasty adjustment by Brown once it became clear the Jarvis amendment would pass. Not only did he switch from all-out opposition to detached ambiguity; he also resumed the anti-government rhetoric of his early, intensely popular days as governor.

That shift may well fulfill what Brown and his political strategists have been seeking: a new approach bringing the governor and his poll ratings out of the doldrums. Ironically, the Jarvis amendment could prove Jerry Brown's salvation, for both reelection this year and his ambitions to replace Jimmy Carter in 1980.

Those ambitions recently had been eclipsed by worries about winning a second term. His closest advisers admitted that the magic of 1975, when Brown entranced a broad spectrum opposing big government and high taxes, had disappeared. Having gradually become the advocate of government programs, he has been sounding more like Nelson Rockefeller than Jerry Brown.

What's more, those same advisers admit the $600,000 statewide media blitz for a Democratic primary campaign in which Brown faced no serious opposition had not really restored his former standing. To the middle class, Brown had become a sectarian advocate against nuclear power, for farm workers, against business and for social reform.

Brown's political touch was particularly shaky on Jarvis. By insisting on tax relief that redistributed income to the poor, he must share with the state legislature blame for inaction that generated irresistible pressure for Jarvis. One of Brown's key advisers conceded to us that, in underestimating chances for Jarvis. "Jerry missed just how much public contempt there is for the political class."

Campaigning vigorously against the Jarvis amendment this spring, Brown committed a rare, unmitigated political blunder. He supported a freeze on higher new property assessments just before the Jarvis vote, a transparent gimmick termed "kindergarten Watergate" by the hot-tempered Jarvis. Facing a personal defeat and the headache of confronting the $7-billion revenue loss, Brown seemed headed for disaster.

Two weeks before the election, Brown abruptly shifted gears. His border-to-border (Mexico-to-Oregon) campaign swing against Jarvis was canceled. Instead, he announced conferences with financial experts to determine strategy following what he now conceded would be the passage of Jarvis.

On a tour of black churches in Los Angeles May 28, Mayor Tom Bradley harangued audiences to vote against Jarvis. But not Brown. He hardly mentioned the issue in the first two churches visited, then in the third church undercut the anti-Jarvis claim that its passage would half vital government services.

"All these things will be done," said Brown, "by the people themselves if not by the government" - a return to his discarded 1976 call for "voluntarism" replacing government. Later that Sunday, addressing a cheering Armenian independence rally of some 7,000, he said not one word about the coming vote.

Brown now talks about "the voice of the people being heard" and promises, "We're going to cut government at all levels." He claims he is best equipped to "cut and squeeze," pledging, "I will add renewed political strength to the government."

Is the people's will on Jarvis not a public message for Jerry Brown to return to anti-government postures of his first two years as governor? "Fine," he replied to us, "then we have a renewed mandate from the people. It [Jarvis] is severely flawed, but we will do it."

That is Brown's theme for the fall campaign and perhaps beyond. Is it remotely possible that Brown would carry to the nation the Jarvis-forced banner of tax reduction and reduced government? "If we respond to this problem effectively," he replied without even the hint of a smile, "the rest of the country would be extremely interested."