President Carter went on the attack against Ronald Reagan's proposed economic policies today and called criticism of his administration's handling of the Stealth airplane project "cheap politics".

Armed with advance word that Reagan was retreating from some of his economic proposals, Carter predicted that the GOP presidential candidate will abandon his support for the Kemp-Roth tax cut plan of 10 percent a year for three years.

In a speech and a meeting with New Jersey editors on campaign trip here, the president said, "There is no way that you can have a Reagan-Kemp-Roth proposal intact, make an attempt to balance the budget, keep a strong defense, to which Reagan professes to be committed, and continue the routine programs that are designed to help the American people have a better life.

"It's just a ridliculous proposal, and any economist who studies it knows that," Carter told the editors.

At the same question-and-answer session, the president made his first response to criticism from Reagan, former president Gerald R. Ford and former secretary of state Henry Kissinger that leaks about the Stealth plane, which is designed to be undetectable by radar, had damaged the nation's security.

"This is an absolutely irresponsible and false charge by Governor Reagan and by a carefully orchestrated group of Republicans," Carter said.

"It's obvious that the Republicans have taken what is a major benefit to our country and tried to play cheap politics with it by alleging that we have violated our nation's security."

Carter said that when he took office he found that the Stealth project -- then in its first stages -- had not been classified by the Ford administration.

There had been congressional testimony on Stealth, Carter said, and a public contract for its development had been let. In the spring of 1977, the Carter administration classified the program, he added.

"The only thing that has been revealed about the Stealth development, which is a major technological evolutionary development for our country, is the existence of the program itself," Carter said, arguing that there had been no security breach as a result of the published stories about the new plane design.

The president, who elaborated on what he told the New Jersey editiors in a later statement to reporters, added that the first published article on Stealth in Aviation Week, on Aug. 11, could not have been a leak from his administration because it was an article criticizing the president for killing the b1 bomber, not an article praising Carter.

Carter's busy 3 1/2-hour vist to Perth Amboy was his first campain trip into a state he lost to Ford in 1976 and badly needs to win this year.

He came here ready to do battle with Reagan on economic issues -- comparing Reagan's economic policies unfavorably with his own economic policy announced less than two week ago.

Reporters were handed a summary of the effects of the Reagan policies prepared by the Office of Management and Budget. The summary argues that Reagan's policies would force either large inflationary budget deficits or the elimination of large numbers of existing federal programs.

A White House official said that basic conclusion was still valid, despite Reagan's alterations of his program, because of the Kemp-Roth tax cut plan, which Reagan reaffirmed today.

Reagan argues that Kemp-Roth would stimulate economic growth that would provide new revenue to make upfor revenue lost through the tax cut.

Carter arrived in a cloud of dust stirred up by his helicopter on a baseball diamond. Several hundred people were crowded along one edge of the field and the president, accompanied by Sen. Bill Bradley and longtime enthusiastic supporter New Jersey Gov. Brendan Byrne, shook hands with many in the crowd before getting back in his helicopter for a short hop to the Raritan River Steel Co.'s new plant.

After donning a hard hat and protective glasses for a tour of the Canadin-owned plant, which converts scrap into steel rods, Carter spoke at the plant's dedication ceremony.

His speech drew only light, occasional applause from the audience of some of the 400 plant workers.

The labor is vital to Carter's chances in New Jersey, where the Democratic Party was bitterly split between the president and Sen. Edward M. Kennedy (D-Mass.) in the primary.

Two prinicipal Kennedy supporters, Essex County Executive Peter Shapiro and Fran Rein, were on hand to welcome Carter to New Jersey. The reunificatin of the party has been slower here than in many other states, however, according to political observers.

Carter received a friendly reception from about 150 state Democratic officials and labor leaders who turned out at the Olive Street Community Center. About 250 people had been invited.

With Byrne and Bradley at his side, Carter compared this year's election to 1968 when the Democratic Party split over the Vietnam war and Richard M. Nixon defeated Hubert H. Humphrey.

"We're making a choice, as we did in 1968, between two futures for America. I can't win without you, but with you we'll win together," Carter told them.