The leaders of the New Jersey Republican Party climbed aboard Ronald Reagan's bandwagon today, giving him pledges of support that their chairman said would translate into at least 55 of the 66 delegates in the June 3 primary.

State GOP Chairman David Norcross, a moderate Republican who backed President Ford in 1976 when Ford won all but four of the New Jersey delegates, said he was convinced Reagan could beat President Carter this year because he was "offering the kind of economic policies that make sense."

Norcross was joined by 17 of the 21 county GOP chairmen in a mass endorsement that assures Reagan the backing of organization delegate slates in all but two of the 15 congressional districts.

James A. Baker III, national campaign chairman for George Bush, said the action was "no surprise" and vowed that Bush would file a full slate of his own delegates in the state. But the decision by GOP leaders in a state where Bush was rated as running even with Reagan two months ago was an indication of the speed with which Reagan's campaign is now rolling.

Baker had met with Norcross and others just a week ago to plead for them to hold off their decision until after Tuesday's Pennsylvania primary, where Bush is making a $1 million last-ditch effort to derail the Reagan bandwagon.

The former California governor picked up the endorsements in a brief stopover at Newark airport and spread the good news among supporters as he campaigned in Philadelphia this afternoon and tonight.

Reagan sandwiched in a tour of the Italian Market between a fund-raising luncheon, a talk to the World Affairs Council and an appearance at the dinner of the Philadelphia Republican Committee, whose support is expected to translate into 13 sure delegates Tuesday.

The fast-moving front-runner began the day in Terre Haute, Ind., where he kicked off his campaigning for the May 6 Indiana primary, where he is virtually unopposed at the moment. Late tonight, he was flying to Bismarck, N.D., to pick up another batch of delegates at Thursday's state GOP convention.

At every stop, Reagan emphasized his appeal for blue-collar Democratic votes by charging that the Carter administration's budget-balancing and anti-inflation policy is deliberately aimed at "putting a million people out of work by the end of this year."

He said the layoffs and shutdowns in automobile plants -- which dominated the headlines in the three cities he visisted today -- are "the result of a deliberate policy by the Carter administration to squeeze the nation into recession at the expense of working men and women."

Reagan said high interest rates have killed auto sales, while federal environmental and safety regulations have added to the costs and competitive disadvantage of domestic producers facing ever-stiffer foreign competition.

It was the economic and regulatory policy of the administration, he said, that "has led the Ford Motor Co. to announce it is closing three plants and is reducing production at four others. It is also threatening the government bail-out loan package put together for Chrysler."

Reagan said he was reluctant to provide relief by import controls on foreign cars of further loan guarantees to companies like Chrysler. He said he would prefer to ease the auto industry's regulatory burden and stimulate the auto market through tax cuts and lowered interest rates.

Norcross said Reagan's economic policy "made sense and offered hope" to voters in industrial states like New Jersey in an election year that he said would be "more like 1932" than any year since the onset of the Great Depression.

The New Jersey chairman said he had been reluctant to support Reagan, because of their differences on such social issues as the Equal Rights Amendment, which Norcross supports and Reagan opposes. But he said he was convinced now that the economic issues would be dominant this fall "and a candidate who talks economic opportunity and doesn't try to cure inflation by promoting unemployment can win blue-collar Democratic votes."

Norcross also conceded that after a brief flurry of interest in Bush, following his victory in the January Iowa caucuses, county organization leaders have been "increasingly eager" to back Reagan for the nomination.