The man who reinstated the Shah; Countercoup: The Struggle for the Control of Iran, by Kermit Roosevelt. New York: McGraw-Hill. $12.95.

Back 1953 Iran, then under increasingly pro-Soviet Prime Minister Mossadegh, seemed to be slipping under the Iron Curtain. But it was evident to Kermit Roosevelt, the Central Intelligence Agency official with prime responsibility for the Near East, that the bulk of the Army and the people themselves were still pro-Shah. The trouble was that the Shah was going through a period of uncertainty and self-doubt.

As Roosevelt tells it at long last in this absorbing narrative, he himself was chosen to mastermind the "countercoup" that would place the monarch back on the Peacock Throne and shear Dr. Mossadegh's powers.

No exploit in the shadowy world of intelligence ever had more exalted sponsorship. Its godparents were President Eisenhower and Winston Churchill, then in his last lap as British prime minister. Because it all seems so long ago and far away, the narrative has a Prisoner-of-Zenda quality, an affinity to Herman Wouk, and shades of Graham Greene. It is all told with style and economy and -- until the very end -- no trace of self- congratulation.

The broad outlines of the episode are well known. It is no revelation that, during those frozen years of the cold war, both superpowers fished where they could in some pretty muddy waters. (Besides, prominent Iranians had beggedm Washington for help, Roosevelt notes.) What is new here is the atmosphere of the way it really was -- the midnight meetings, near-betrayals, last-minute hazards before the final triumph.

After a hegira to Rome, the Shah would soon have reached the point of no return, had Roosevelt not orchestrated his triumphant homecoming to Tehran through the series of maneuvers fascinatingly recounted here.

Two quotes are revealing of Roosevelt's quiet pride in what he achieved: After it was all over, the Shah told him, "I owe my throne to God, my people, my Army, and to you." The "you," the author reminds us, really meant the two countries he represented. Last of all, on his way back to the US, Roosevelt had a debriefing at the bedside of Winston Churchill, who dozed fitfully during the report. At the end, Churchill roused himself and said, "Young man, if I had been but a few years younger, I would have loved nothing better than have served under your command in this great venture."

Such accolades should not go unrecorded. "Countercoup" belongs on a shelf with the very best true tales of derring-do.