LOS ANGELES -- Sen. Pete Wilson returned to Washington last week at his opponent's prodding to perform Capitol Hill duties, but only reluctantly and briefly. That's because he has forged ahead for governor by telling Californians that, after a lifetime of public service, he is not part of the despised political establishment.

This agility was facilitated by Wilson's recent break with the state Republican establishment to back a referendum limiting state legislative terms. He thereby forced his Democratic foe, ex-San Francisco mayor Dianne Feinstein, into an unwanted defense of the Sacramento gang.

There is no proof of cause and effect, but Wilson's support of term limits coincides with his breakaway from a 4-month-old dead heat to take a lead estimated at five to seven points. The buttoned-down senator may be miscast as a populist, but the issue puts him astride a ground swell.

Issues are rarely discussed in this most important campaign of 1990. Who becomes governor of the nation's biggest state may determine up to 25 seats in Congress after next year's redistricting. Yet that political impact is never mentioned as each woos the nonparty voter. In fact, the two candidates are in wide agreement: pro-capital punishment, extremist on abortion rights, loudly pro-environment and anti-crime. Each has spent a lifetime in public office, and neither can disguise inherent belief in the governmental and political process.

That makes both ill-equipped to take advantage of what their pollsters tell them: voters here, as elsewhere, are alienated from government and politics and demand "change." Through the spring and summer, Feinstein -- tall, handsome, a person who fills a room when her pale opponent seems lost in it -- as the fresh personality seemed the candidate of change. In fact, she is as scrupulously moderate and conventional as her opponent.

But Wilson two weeks ago broke away to endorse term limits, a move encouraged by Vice President Dan Quayle. Wilson was at the side of his old Senate pal, Quayle, who was touring California three weeks ago and evoking enthusiastic crowd responses when for the first time he publicly endorsed term limits.

Wilson's stand infuriated the Republican power structure, especially State Senate Leader Ken Maddy (no admirer of Wilson anyway). As with the Proposition 13 tax cut in 1978, the GOP minority is in league with Speaker Willie Brown and the Democratic majority to maintain the status quo.

Only six of 13 State Assembly Republicans support the proposition, and even Wilson's running mate for lieutenant governor opposes it. Brown is tapping Republican-oriented corporations, developers and lobbyists -- all of whom want no new crew in Sacramento -- to build a $4 million war chest for a late TV blitz to defeat term limitations.

Feinstein was urged by some advisers to join Wilson in defying the establishment. She did not, and not merely because it would antagonize her good friend and powerful supporter, Willie Brown. She is at heart an orthodox politician, who told us she was impeded as mayor by a two-term limit. Instead of neutralizing Wilson's stand by echoing it, she called him a "weather vane" for joining the public cry. That enabled Wilson to link her more tightly to Brown, who shows up with statewide negative ratings in the polls.

Feinstein's handlers are doubly frustrated by an inability to identify Wilson with the status quo. "Our focus groups show they don't even know he's a senator," a Feinstein aide complained. That explains her recent emphasis on charging that Wilson was shirking his duties in the Senate.

With discussion of issues no more serious here than elsewhere, Californians will pick their governor (and, indirectly, a good many congressmen) by deciding who's for change. Pete Wilson has recognized the public mood by telling the Sacramento gang to get out of town.