he campaign of Rep. Barry M. Goldwater Jr. (R-Calif.) to join his father in the Senate has taken its worst blow to date with the release of a major independent poll showing him in third place in the Republican state primary.

With California's most expensive primary race ever heading into the final weekend, Mervin Field's California Poll revealed a startling reversal of a 16 percentage-point lead Goldwater held over his two closest rivals in January.

The poll of 359 likely GOP voters in the last week of the campaign showed San Diego Mayor Pete Wilson leading with 33 percent, Rep. Paul N. (Pete) McCloskey with 21 percent and Goldwater with 19 percent.

Officials in several campaigns attributed Goldwater's decline to his refusal to participate in several public debates with a large field of Republican opponents and confront the damaging accusation that he lacked the mental agility to beat the likely Democratic nominee, Gov. Edmund G. (Jerry) Brown Jr.

Noting that Goldwater sought to ignore his Republican opponents and profit from GOP voter affection for his father, conservative patriarch Sen. Barry Goldwater (R-Ariz.), McCloskey said at UCLA this week: "If he were half the man his father is, he'd be leading us all 2 to 1."

Goldwater also appeared to suffer from a late start in television advertising and from Wilson's unexpected success in winning support from conservatives after years of losing primary campaigns for governor because of his reputation as a "moderate".

In this race, Wilson has taken consistently conservative, pro-Reagan stands. He opposed federally-funded abortions, rent control and the popular bilateral nuclear weapons freeze. His campaign also broadcast an endorsement from Neil Reagan calling Wilson "a loyal supporter of my brother, the president."

Wilson's campaign press director, Otto Bos, credited Wilson's surge to his 10-year record as a popular and effective mayor. "People are tired of talk, they want a track record," Bos said. He said Wilson's polls showed at least an 8-point Wilson lead over Goldwater and McCloskey.

Goldwater's campaign coordinator, Ben D. Key, challenged the accuracy of Field's poll because of its small sample size. Polls of that size have about a 6 percent margin of error either way, and Wilson's lead theoretically could be as much as 12 points less than is shown, he said.

Key said Goldwater's polls, done by Reagan presidential campaign pollster Richard Wirthlin, showed the three leaders to be very close. "It's going to be a horse race all the way," Key said.

McCloskey's campaign manager, Ron Smith, said his polls also showed the top three much closer than the Field poll indicated. "We think we can pull it out in the last three days," Smith said.

McCloskey, unlike Wilson, has made little effort to shed his own moderate image. McCloskey supported gun control and a nuclear freeze while embracing Reaganomics and coming out in the last week against the proposed California peripheral canal.

The canal project would bring more water to southern California, and has been supported by Wilson and other politicians from the southern part of the state, but Field's poll shows it losing by 49 to 30 percent on this Tuesday's ballot.

A loss by Goldwater would be bad news for Democrat Brown, who trails all three top Republicans in the polls but appeared to have the best chance at beating Goldwater. Field's trial heat poll showed Wilson beating Brown by 22 points, McCloskey beating him by 25 points and Goldwater beating him by 12 points.

In Brown's primary race, Field's poll showed him with 46 percent to 12 percent for novelist Gore Vidal, 9 percent for State Sen. Paul Carpenter and 7 percent for Fresno Mayor Dan Whitehurst.

Trailing the three Republican front-runners in the Field poll were businesswoman and broadcaster Maureen Reagan, the president's daughter, with 5 percent, Rep. Robert K. Dornan with 3 percent and businessman Ted Bruinsma with 2 percent. The endorsement of Bruinsma by retiring Republican Sen. S.I. Hayakawa appeared to have little effect on the campaign.

Goldwater this week made a last effort to overcome Wilson's apparently widening lead by scrapping bland TV and radio ads and introducing an anti-Wilson message.

"In 1976, I supported Ronald Reagan for president. Pete Wilson and Jerry Brown were attacking him," Goldwater says in a new TV commercial. "In 1978, I campaigned for Proposition 13. Wilson and Brown opposed it." Wilson immediately accused Goldwater of "smear charges."

In the gubernatorial primaries, Field's poll showed Republican Lt. Gov. Mike Curb leading Republican Attorney General George Deukmejian by 47 to 40 percent. Field attributed Curb's lead to a successful gamble in coming out against the peripheral canal despite what was originally thought to have been widespread support for the project in populous Southern California.

In the Democratic gubernatorial primary, Los Angeles Mayor Tom Bradley--who leads both Curb and Deukmejian in trial heats--appears to have his victory assured with 62 percent of 429 Democrats polled against 15 percent for State Senate Majority Leader John Garamendi and 5 percent for former state health and welfare secretary Mario Obledo.