A federal judge in Trenton N.J., revoked the probation yesterday of an anti-Castro Cuban exile who has been charged with conspiracy to murder former Chilean ambassador Orlando Letelier.

As a result of the revocation, Guillermo Novo Sampol must serve the remaining 2 1/2 years of a three-year prison term that was imposed by U.S. District Judge George Barlow in 1974 on a charge of conspiring to bomb a Cuban ship.

The revocation of Novo's probation was asked by federal investigators who have been probing the bomb-murder of Letelier for the last 20 months. The original request that Novo's probation be revoked came last June, but Novo failed to show up for a hearing then and became a fugitive.

Novo was arrested in Miami on a fugitive charge about three weeks ago, as was Alvin Ross Diaz.

Novo's probation was revoked after investigators said they had learned that he had traveled to Chile and Venezuela without permission of his probation officer, in violation of the terms of his probation Assistant U.S. Attorneys Eugene M. Propper and E. Lawrence Barcella Jr. of Washington's major crimes division said yesterday in Trenton that they had received information from Venezuela's secret police, known as DISIP, that Novo had met with Cuban exile leader Orlando Bosch in Venezuela in late 1974.

A high DISIP official said Novo conceded at the time that he was not supposed to be out of the U.S. and said he would "throw his passport into a river" to avoid detection, agents said yesterday.

The investigators said Jose Dionisio Suarez Esquivel, another person charged in the Letelier case, also met with Bosch in Venezuela. In addition, Novo and Suarez traveled to Chile during the same late-1974 trip, it was disclosed in court.