To the surprise of his friends and the consternation of his opponents, "old politician" Evelle J. Younger has suddenly emerged as a formidable challenge to "new politician" Edmund G. (Jerry) Brown Jr.

Before he gets ready to tackle Gov. Brown, who is assured of renomination in Tuesday's primary, Attorney General Younger will have to win a four-way battle for the Republican gubernatorial nomination. But again, to the surprise of many politicians, Younger is clinging to a lead over opponents who have more charm, style and money than he does.

The final voter survey by veteran California pollster Mervin Field before the primary election shows Younger running only 1 percent point behind Brown, who led Younger by 28 points in an October trial heat. Field said he believes that "Brown is in serious trouble," largely because the governor has strongly identified himself with efforts to stop Proposition 13, a property tax rollback initiative which is running far ahead in the polls.

In the Republican primary race, according to the figures of Field's "California Poll," Younger leads with 31 percent of the vote. Trailing him are former Los Angeles police chief Ed Davis, with 27 percent, state Assemblyman Ken Maddy of Fresno with 21 percent, and San Diego Mayor Pete Wilson, with 6 percent. The other 15 percent of the voters are undecided, according to Field survey.

With this many undecided voters, the election is too close to call for Younger, especially since the ultra conservatives who support Davis usually vote in disproportionately high numbers in California GOP primaries.

But many Republicans did not even expect Younger to be in the race by this time, much less leading. Starting with a 42-to-17 lead over Davis in march 1977, Younger dropped steadily for the next 14 months and in May led Davis by only 2 percentage points.

Every time a poll came out, Younger's supporters would say that their candidate had "bottomed out." Every time, he would instead drop a few more percentage points.

Actually, Younger probably was never as far ahead as it seemed. As the only Republican state officeholder in heavily Democratic California, Younger's early lead probably reflected his high name recognition among GOP voters more than anything else.

Survey's showed that Younger, a poor stump speaker who can be effective in the give-and-take of a news conference, produced a very low emotional response among voters, but was generally trusted and respected. The primary campaign has been based on this knowledge. Younger has almost reveled in his image as a plodder, telling reporters that he didn't excite anybody but hoped that voters considered him trustworthy and competent.

"Dull is beautiful," said Younger's campaign manager, Ken Reitz, and he may be right. In the early handicapping of the election, Younger was supposed to be at a disadvantage to the quotable Davis and the telegenic, if lesser-known Maddy, but it hasn't worked that way.

Though Republicans have stayed from Younger's rallies in droves, and though he has raised less money (about $1 million) than any of the other GOP candidates, Younger has stayed ahead in the published polls.

Aware that Younger was known to nearly every voter, his campaign strategists were able to take the calculated risk of waiting out his opponent. Davis received early recognition because of his broadside attacks against Brown; Maddy weighed in strongly early in the year with an expensive television campaign that billed him as the one man who could beat Brown.

Younger waited, saving his money for a television campaign at the end and relying on the knowledge that voters, while they may not warm to him emotionally, have a generally positive view of his performance.

This waiting game was helped by Younger's self-confidence, which is enhanced by the fact that he has never lost an election. As a former FBI agent, Judge, district attorney and attorney general for eight years, Younger has developed a reputation as a patient, even over-cautious, lawyer who takes few political chances but usually runs ahead of other Republicans.

Younger was a long-shot candidate to beat Brown when he started. The fact that he is a formidable challenger now is as much due to Brown's slump in voter approval as it is to Younger's gain.

Pollster Field says he thinks that Brown may now be seen as "just another politician" by voters after waging an expensive and unnecessary primary campaign and becoming identified with attempts to stop Proposition 13.

Maddy, also, was damaged by his stand against Proposition 13, especially since it is supported almost 3 to 1 by Republican voters.

Davis loudly endorsed Proposition 13, as did John Briggs, a conservative who dropped out of the race and backed Davis after briggs failed to attract voter support. Younger, characteristically, backed Proposition 13 in muted terms, but spent a good part of various news conferences pointing out deficiencies in the measure.

Both Reitz and Davis' campaign manager, mark barnes, agree that one irony of the race is that Davis, the staunchest backer of the tax-limitation initiative, might wind up being hurt by it.

That's because the measure seems certain to guarantee a large turnout - 68 percent of all voters, according to Secretary of State March Fong Eu's estimate, with the likely Republican turnout much higher - and that means the participation of many "casual" voters who are less committed to Davis than the conservatives who always vote in California primaries.

Younger's biggest problem is that he continues to divide the moderate vote with Maddy, creating the theoretical possibility that Davis may slip into the nomination. One of Davis' silent boosters Tuesday undoubtedly will be Brown, who leads the former police chief by 17 points in Field's latest trial heat.