Republican presidential nominee Ronald Reagan charged today that the Carter administration has dealt the United States a "grievous blow" by leaking highly secret details about the "Stealth" aircraft project for political purposes -- and that the disclosure has given the Soviets a 10-year head start in developing counter-measures.

In a blistering attack aimed at regaining the campaign offensive, Reagan said that unnamed military officials "who have served this nation in the very highest capacities tell me they cannot recall such a serious breach of national security secrets."

Reagan charged that Defense Secretary Harold Brown, in disclosing the Stealth project that will make U.S. planes invisible to radar detection, "has breached one of the nation's most closely held military secrets in a transparent effort to divert attention from the administration's dismal defense record."

Reagan leveled his politically explosive accusations in a speech to the Combines Businessmen'sClub luncheon, then repeated it before a large crowd at an outdoor park ralley.

"The law provides severe penalties for anyone violating military weapons secrets of this magnitude," Reagan said. "In this case, because the breach of secrecy was blessed and sanctioned by the Carter administration itself -- clearly for the sole political purpose of aiding Mr. Carter's troubled campaign -- there will be no such penalty. But, the fact remains, it has dealt the nation a grievous blow."

Reagan's charge was based heavily upon recent congressional testimony by the editor of the Armed Forces Journal, Benjamin F. Schemmer, who described how he received and published details about the Stealth technology.

Reagan said Schemmer told the House Armed Services subcommittee on research and development that he had been summoned by undersecretary of defense William Perry, who gave him the Stealth information and urged him to publish it. Four days after that meeting, said Reagan, the secretary of defense called a press conference to say that because there had been "leaks" to the press, it was no longer "appropriate or credible" to maintain the secrecy of the Stealth project. Brown then outlined the program for reporters.

In his testimony, Schemmer called the Defense Department's leak to him "irresponsible," Reagan said. He also quoted the editor as saying he believed the information had been given to him, to be made public, for "political purposes."

Disclosure of the Stealth project, Reagan said, significantly benefitted Soviet military planners. "Since the Stealth aircraft would not have been ready for use until the 1980s the Carter administration's action has now given the Kremlin a 10-year head-start on developing ways to counter this type of ultra-sophisticated weapons systems," Reagan said. "The KGB is no doubt gleefully celebrating this unearned triumph."

While the candidate portrayed the disclosure as part of a calculated Carter political plan, Reagan aides said they did not know who ordered the information made public. "But presumably it came from someone of high authority," said Reagan's chief national security adviser, Richard Allen.

Allen said that Reagan campaign officals had heard "some talk" in recent weeks about the possibility that Carter officials planned to leak the information on the Stealth project but that the Reagan officials had no firm advance knowledge of any plan to make the information public.

Allen also said that the Stealth disclosure seemed to parallel a case in election-year 1964, when the Johnson administration made public information about the SR71 reconnaissance plane.

Reagan called the details of the Stealth project "some of the most tightly classified, most highly secret weapons information since the Manhattan project." He added: "I understand the Stealth project was so secret that some of the civilians working on it had to agree to allow the government to tap their phones."

Warming to the attack, Reagan went on:

"This kind of blatant politicalization of the Department of Defense has left a dark blot on the proud traditions of the Pentagon . . . but, worst of all, the administration's decision to disclose and the exploit for political purposes this super-secret technology, in an effort to blur its dismal defense record, is a cynical misuse of power and a clear abuse of the public trust."

Reagan had set out for his day of campaigning in Jacksonville and New Orleans with his candidacy jarred by a series of recent small, but damaging, oratorical gaffes. The most recent was Reagan's attempt to link Carter with the Ku Klux Klan because the president had chosen to open his own campaign in Alabama. Reagan opologized indirectly in a written statement the next day. Reagan campaign aides are still exploring whether the gaffe will cost Reagan his chance of cutting into Carter's southern base of support.

At Reagan's two appearances today there were no signs of political fallout, although such signs are not always visible at political rallies. Reagan was greeted by prolonged applause at the businessmen's luncheon, and the crowd in the park responded with enthusiasm that was perhaps stifled by the heat and humidity.

Reagan aides have been concerned that the challenger has been on the defensive more than the incumbent in these first weeks.

"Now maybe the White House has some things to explain for a change," said a senior Reagan aide.

Before leaving Jacksonville, Reagan was asked whether his comment about the Klan would affect his campaign in Florida and the South. "No, I'm not going to respond to the president's personal attack on me," Reagan said. "I'm going to continue to deal with issues, which is what he has done to the economy, with unemployment and inflation."