It envisions the defeat of the contras by 1990, after which the United States, with its long history of intervention in Central America, may invade Nicaragua.

This, they said, would give Mr. Reagan a pretext to recognize the contras as the legitimate government and to come to its aid by invading Nicaragua.

The defector, Maj. Roger Miranda Bengoechea, told American journalists that if the United States invaded Nicaragua, the Sandinista Government would try to "regionalize the conflict."

As to how Cuba might react should the United States invade Nicaragua - a subject of frequent speculation in Latin America - he said he had no information.

It soon becomes apparent that the lawyer and the mysterious audio cassette have something to do with financing the contras in their attempts to invade Nicaragua.

The official said Argentina was actually training the contras to invade Nicaragua and wrest control of the government from the Sandinistas.

This would be accompanied by an announcement that the United States did not intend to invade Nicaragua but that no more arms deliveries of such weapons would be permitted.

Professor Carter recalled that a California lawyer named William Walker organized a force of some 60 men who invaded Nicaragua in 1855 with dreams of creating an empire throughout Central America.

No Plan for Taking Hostages Mr. Ortega denied having plans to attack neighboring governments or to take Americans hostage if the United States invaded Nicaragua.

Another State Department official said, "We're not going to invade Nicaragua even if the Sandinistas are standing there with a smoking gun."