Members of the Cuban Nationalist Movement, a New Jersey-based, anti-Castro group of Cuban exiles, ran counter surveillance operations against the FBI as it investigated the 1976 assassination of former Chilean ambassador Orlando Letelier, an FBI agent testified yesterday.

Agent Larry E. Wack told a U.S. District Court jury hearing the case against three Cuban exiles charged in connection with the Letelier slaying that paid FBI informant Ricardo Canete told him that one of the defendants in the case, Ignacio Novo Sampol, showed Canete a picture that Cuban Nationalists had taken of Wack.

At the time, during 1977 and 1978, Wack said he was directing Canete's operations as an informant trying to learn information about the Letelier killing from Novo another defendant in the case Alvin Ross Diaz.

Wack conceded under cross-examination, however, that he had not seen the photograph.

Canete, who has been convicted of larceny and counterfeit money charges, testified Tuesday that Ross bragged to him that he "made Letelier's bomb" and that he furnished extensive false identification documents to Novo at his request.

The seven-woman, five-man jury heard little testimony yesterday -- the 17th day of the trial -- as prosecution and defense attorneys spent most of the afternoon arguing about the admissibility of testimony from two jailmates of Ross and the third defendant in the case, Guillermo Novo Sampol.

Judge Barrington D. Parker said he would hear more arguments on the issue this morning before making a ruling.