A leftist terrorist group has claimed responsibility for Friday's ambush killing of four Americans outside Istanbul and linked the deaths to the situation in Iran, police reported yesterday.

Police said the group, calling itself the Marxist-Leninist Armed Propaganda Squad, telephoned Turkish newspapers and agencies to claim responsibility.

A phone caller was quoted as saying the attack was aimed at "exposing American imperialism in general and the plots to suppress the people's movement in the Middle East and Iran in particular."

The victims have been identified as U.S. Army Sgt. James Smith, 40, and three civilian employes of a Boeing Aircraft Co. subsidiary: Jim Clark, 63, Robert Frantz, 48, and Elmer Cooper, 65. Frantz previously had been identified incorrectly as Robert French. The Turkish driver of the Americans' private minibus, Kamil Korkmaz, was wounded.

The men were shot as they left their jobs at the nearby Cakmakli military base.

Turkish Prime Minister Suleyman Demirel said in a statement that he was "deeply grieved" by the killings.He called them "a new example of the continuous storm of banditry, cruelty and murder" in Turkey and called on the nation to help him stamp it out.

Turkish police began an extensive search for the killer, and press reports said they were arresting suspects.