The dossier submitted by the United States to Chile on the assassination of Orlando Letelier reportedly contains charges that the Chilean secret police had a longstanding relationship with Cuban exile terrorists and sent some of them as hit men on unsuccessful missions to kill four other prominent Chilean exiles.

A lawyer who studied the documents has disclosed that the dossier also establishes that Michael Townley, the Chilean agent who has confessed to a role in the Letelier murder, was in Buenos Aires in 1974 when an exiled Chilean general and his wife were blown up with a car bomb and was in Rome in 1975 when an exiled political leader and his wife were seriously wounded by a gunman.

The dossier of FBI evidence is the case was declared secret by a Chilean court after it was presented last month to back up the U.S. request that Chile extradite three army officers. The officers include retired Gen. Manuel Contreras, who headed DINA, the Chilean secret police, when Letelier was killed in a car bombing in Washington in September 1976.

A federal grand jury returned a murder indictment in August against Contreras, Col. Pedro Espinoza, DINA chief of operations in 1876, Capt. Armando Fernandez, a DINA operative, and five members of the New Jersey based Cuban Nationalist Movement, an anti-Castro exile group.

A Chilean lawyer who said he had access to the dossier and had carefully studied it agreed to summarize on the contents of the U.S. evidence. Other sources confirmed that the lawyer had first-hand knowledge of the dossier.

The documents - about 700 pages of testimony as well as films - are intended to prove the U.S. charges that Contreas and Espinoza, as DINA officers, ordered Townley and Fernandez to carry out the Letelier assassination with the Cubans' help.

Despite the secrecy rule, the U.S. dossier is known to have been copied in the Chilean Foreign Ministry before being handed on to the Chilean court. Gen. Contreras has one copy, accordint to persons who said they saw him and his lawyer studying the documents at the Military Hospital where the three defendants are being held under preventive arrest.

According to the lawyer's summary, the U.S. documents include:

Statements to the FBI that the DINA sent Cubans on unsuccessful assassination missions in 1975 and 1976 against Chilean Christian Democratic leader Gabriel Valdes in New York, Socialist Party General Secretary Carlos Altamirano in Mexico, and Leftist Revolutionary Movement (knows as MIR) leaders Pascal Allende and Mary Anne Beausire in Costa Rica.

Testimony by Mariana Callejas, Townley's wife and also a DINA agent, that she and Townley were in Buenos Aires, Argentina, in September 1974. The visit coincided with the car bombinh thered that killed retired Chilean Gen. Carlos Prats, a former commander in chief of the army, and his wife in an assassination similar to the Letelier murder.

Callejas' testimony that she and Townley also traveled to Rome in October 1975 - at the time of an assassination attempt against Chilean exile Bernardo Leighton, a leader of the opposition Christian Democratic Party. Leighton and his wife were both seriously wounded in the attack on a Rome street and she remains partially paralzed.

Testimony by Townley that pilots and other employees of LAN Chile, the government-owned airline, carried packages containing explosives and bomb parts back and fourth between Townley in Chile and Cubans in the United States.

Townley, an American expatriate who has lived most of the last 20 years in Chile, was expelled from Chile in April and turned over to the FBI. He is cooperating with the investigation. In a plea-bargaining arrangement, he pleaded guilty to one count of conspiracy to murder Letelier.

His statement describing the assassination, which he said his DINA superiors ordered him to arrange and carry out, is a major part of the dossier. Many of the details are corroborated by Callejas' testimony.

Callejas, a Chilean, was on the DINA payroll with her husband, and is mentioned in the U.S. indictment as having passed on messages of the assassination preparations in Washington.

The Leighton and Prats cases are not mentioned as such in the dossier, the source said. Callejas simply states the dates of her trips with Townley.

There have been a number of unconfirmed reports that Townley has told the FBI that he was involved in those crimes. Part of Townley's plea-bargaining, Townley's wife said in an interview some time ago, is that his family will be protected and that Townley will not be required to testify in connection with terrorist activities other than the Letelier murder.

The source of much of the information in the dossier about the Chilean-Cuban connection is Rolando Otero, a Cuban exile and Bay of Ripgs veteran with a long history of terrorist activities against the Cuban government.

Otero, who is serving a prison term in Florida for exploding a bomb in Miami International airport in 1975, said he was in Chile for long periods in 1976 receiving training from DINA, according to the lawyer.

Otero, the source said, told the FBI he was sent to Costa Rica in early 1976 to assassinate Beausire and Pascal Allende - the nephew of former president Salvador Allende, a socialist who was overthrown in 1973 by the present military government. The two MIR leaders had been given asylum in Costa Rica after escapting a DINA manhunt in late 1975.

Otereo's mission failed apparently because Allende and Beausire left for Cuba before he could carry out his assassination plan, the source said. Otereo, who the source said told the FBI the Chilean-Cuban connection began to take shape shortly after the September 1973 coup, later expelled by Chile and turned over to the FBI.

The source said the mission to kill Altamirano in Mexico in 1975 was entrusted by DINA to members of the Cuban Nationalist Movement, the same group that is alleged to have assisted "Townley in the Letelier assassination, but did not say why that mission was unsuccessful.