Sen. Jesse Helms (R-N.C.) has accused the State Department and the Central Intelligence Agency of planning "a betrayal" of President Reagan's policy in Central America and antigovernment rebels in Nicaragua.

In what his aides described as a major policy statement, Helms, chairman of the Foreign Relations subcommittee on Western Hemisphere affairs, charged that the State Department and the CIA "have continued to assume that the [leftist] Sandinista revolution is fundamentally beneficial to Nicaragua," and that they have "a mania for negotiations" with Nicaragua as the way to end its involvement with Cuba and the Soviet Union.

Helms made his charges in a floor statement Thursday night.

A senior State Department official characterized the speech as "nonsense." Spokesmen for the department and for the CIA said there would be no formal response.

Instead of backing the "freedom fighters," the State Department is trying to "impose" on them new leaders they do not want -- disaffected former Sandinista ambassador Arturo Cruz and the Costa Rica-based dissident group he heads called "Nicaraguan Resistance," Helms said.

"The State Department clearly appears to have concocted a new plan amounting to a betrayal of not only the freedom fighters but also the desire of President Reagan to see freedom established in Nicaragua," Helms said. "President Reagan and the people of Nicaragua must not be betrayed."

Cruz's philosophy "can hardly be distinguished from the Marxist orientation of the Sandinistas," Helms said. He said the Cruz group's March 3 manifesto, signed in Costa Rica and endorsed by the State Department, was forced on many of the rebels by the CIA and is "a blueprint for fuzzy-minded socialism."

"One doesn't know whether to laugh or to weep," Helms said. "I do not know whether it was conceived and drafted by the CIA or by the Sandinistas."

The speech, which took up nearly four pages of yesterday's Congressional Record, reflects the extreme conservative view that "Reagan is being undercut by low-level diplomats who are trying to sell him out and cut a deal with Nicaragua," a Helms aide said.

Reagan is expected to seek $14 million from Congress for the CIA to provide further military aid to the rebels, but the aide said the State Department and the CIA appear to be planning to ask Congress to fund the Cruz group instead.

"They told at least one of the freedom fighters that if they didn't get on this train [by signing the March 3 manifesto] there wouldn't be any other train," the aide said.

The Nicaraguan Resistance manifesto, signed by Cruz and 50 Nicaraguan businessmen, politicians and rebel groups -- including the largest, the Nicaraguan Democratic Force -- offers the Sandinistas a cease-fire and continued control of the presidency in return for new elections, amnesty, removal of foreign troops and military advisers, and other measures to be guaranteed by the Nicaraguan Roman Catholic bishops and other Central American governments.

The terms "are lopsided in favor of the continuance of the Sandinista regime," Helms said.