The House and Senate intelligence committees have asked the Defense Department to produce copies of Vietnam-era psychological-warfare training manuals to determine whether at least one may recommend political assassination in language like that in a manual distributed to anti-Sandinista rebels in Nicaragua.

Committee officials said they had obtained partial copies of an apparent U.S. Army manual dated April 1968, produced at Fort Bragg, N.C., that includes sections "almost word for word" the same in translation as controversial parts of a manual the Central Intelligence Agency distributed in Spanish last year to the Nicaraguan rebels.

That 90-page Spanish booklet, called "Psychological Operations in Guerrilla War," advocated the "selective use of violence" to "neutralize" judges, doctors and public officials of the leftist Sandinista government of Nicaragua.

Although President Reagan last week disavowed such tactics and launched investigations of the manual's origins, conflicting reports of its genesis and use caused a firestorm in Congress.

At issue is the degree to which the United States is willing to engage in violence, by its own agents or surrogates, against political figures of governments with which it technically is at peace.

The committees have asked the CIA to produce the Nicaraguan manual's author at hearings starting next week to explain his work and the sources of his recommendations. Edgar Chamorro, a director of the Nicaraguan Democratic Force (FDN), the largest rebel group, has said the manual was based on U.S. Army and CIA field manuals dating from the 1960s.

He said the manual was poorly translated into Spanish by a CIA operative in Honduras who called himself John Kirkpatrick. However, Washington investigators said the author was a different person, operating out of CIA headquarters at Langley. They said the manual had been cleared only by middle-level CIA officials, some of whom did not speak Spanish.

Current field manuals on psychological operations, in use at Fort Bragg's Special Warfare Center, embody official U.S. government policy on guerrilla methods. They make no reference to violent "neutralizing " techniques. The fragmentary 1968 document obtained by the intelligence committees, however, does contain such language, committee officials said.

A senior Defense Department official said it was possible that such a manual "may have existed" under President Lyndon B. Johnson but noted that there was no special presidential order barring political assassinations until Reagan issued one in December 1981.

Also at issue is the range of activity Congress thinks it is authorizing when it approves any kind of covert military action anywhere in the world.

Although Reagan set up the Nicaragua program ostensibly to block supplies to leftist rebels in El Salvador, the Nicaraguan insurgents make no secret that their goal is to overthrow the Sandinista government, an objective the Reagan administration has disavowed.