John C. Platt, a Central Intelligence Agency officer who forged a remarkable and secret friendship with a Soviet K.G.B. agent in the midst of the Cold War, only to see their friendship betrayed by a Russian mole inside the C.I.A., died on Jan. 4 at his home in Potomac Falls, Va. He was 80.

His wife, Paige Platt, said the cause was esophageal cancer.

Mr. Platt, who was known as Jack, was a gruff former Marine officer who for years ran a training program in Washington to teach C.I.A. case officers how to operate under cover. But he was best known in the spy world for his longtime friendship with Gennadiy Vasilenko, a K.G.B. officer whose betrayal by Aldrich Ames, the Soviet mole at the C.I.A., led to Mr. Vasilenko’s imprisonment in Moscow.

Mr. Platt, who had joined the C.I.A. in 1963, met Mr. Vasilenko in the late 1970s while he was based in Washington, where he was trying to identify and meet K.G.B. officers posted there with the aim of recruiting them to spy for the United States.

In 1977, a Soviet defector told Mr. Platt that one of his classmates from the K.G.B.’s training institute was working under diplomatic cover at the Soviet Embassy in Washington. The classmate he identified was Mr. Vasilenko.