The F.B.I. tried to track suspected associates of Chilean leftists in the United States in the 1970's on behalf of the Government of Gen. Augusto Pinochet, the Chilean dictator, newly declassified documents show.

The Federal Bureau of Investigation sent agents in New York and Dallas to search for two people whose names were found in the address book of a courier for an underground Marxist group in Chile. The courier was arrested in Paraguay in 1975, and the Paraguayan police passed on the information to American officials, the records show.

''The F.B.I. initiated an investigation in the United States of the aforementioned people and addresses,'' the bureau's legal attache in Buenos Aires wrote to a senior Chilean official in June 1975. ''I will inform you of the results of the investigation as soon as I have them in hand.''

Nothing came of the investigations detailed in the documents. The bureau could not find the people it was looking for and closed the case. Their nationalities and whereabouts are unknown.