EATTLE — On the brink of war, both supporters and critics of United States policy on Iraq agree on the origins, at least, of the haunted relations that have brought us to this pass: America's dealings with Saddam Hussein, justifiable or not, began some two decades ago with its shadowy, expedient support of his regime in the Iraq-Iran war of the 1980's.

Both sides are mistaken. Washington's policy traces an even longer, more shrouded and fateful history. Forty years ago, the Central Intelligence Agency, under President John F. Kennedy, conducted its own regime change in Baghdad, carried out in collaboration with Saddam Hussein.

The Iraqi leader seen as a grave threat in 1963 was Abdel Karim Kassem, a general who five years earlier had deposed the Western-allied Iraqi monarchy. Washington's role in the coup went unreported at the time and has been little noted since. America's anti-Kassem intrigue has been widely substantiated, however, in disclosures by the Senate Committee on Intelligence and in the work of journalists and historians like David Wise, an authority on the C.I.A.

From 1958 to 1960, despite Kassem's harsh repression, the Eisenhower administration abided him as a counter to Washington's Arab nemesis of the era, Gamal Abdel Nasser of Egypt — much as Ronald Reagan and George H. W. Bush would aid Saddam Hussein in the 1980's against the common foe of Iran. By 1961, the Kassem regime had grown more assertive. Seeking new arms rivaling Israel's arsenal, threatening Western oil interests, resuming his country's old quarrel with Kuwait, talking openly of challenging the dominance of America in the Middle East — all steps Saddam Hussein was to repeat in some form — Kassem was regarded by Washington as a dangerous leader who must be removed.

In 1963 Britain and Israel backed American intervention in Iraq, while other United States allies — chiefly France and Germany — resisted. But without significant opposition within the government, Kennedy, like President Bush today, pressed on. In Cairo, Damascus, Tehran and Baghdad, American agents marshaled opponents of the Iraqi regime. Washington set up a base of operations in Kuwait, intercepting Iraqi communications and radioing orders to rebels. The United States armed Kurdish insurgents. The C.I.A.'s "Health Alteration Committee," as it was tactfully called, sent Kassem a monogrammed, poisoned handkerchief, though the potentially lethal gift either failed to work or never reached its victim.

Then, on Feb. 8, 1963, the conspirators staged a coup in Baghdad. For a time the government held out, but eventually Kassem gave up, and after a swift trial was shot; his body was later shown on Baghdad television. Washington immediately befriended the successor regime. "Almost certainly a gain for our side," Robert Komer, a National Security Council aide, wrote to Kennedy the day of the takeover.

As its instrument the C.I.A. had chosen the authoritarian and anti-Communist Baath Party, in 1963 still a relatively small political faction influential in the Iraqi Army. According to the former Baathist leader Hani Fkaiki, among party members colluding with the C.I.A. in 1962 and 1963 was Saddam Hussein, then a 25-year-old who had fled to Cairo after taking part in a failed assassination of Kassem in 1958.

According to Western scholars, as well as Iraqi refugees and a British human rights organization, the 1963 coup was accompanied by a bloodbath. Using lists of suspected Communists and other leftists provided by the C.I.A., the Baathists systematically murdered untold numbers of Iraq's educated elite — killings in which Saddam Hussein himself is said to have participated. No one knows the exact toll, but accounts agree that the victims included hundreds of doctors, teachers, technicians, lawyers and other professionals as well as military and political figures.

The United States also sent arms to the new regime, weapons later used against the same Kurdish insurgents the United States had backed against Kassem and then abandoned. Soon, Western corporations like Mobil, Bechtel and British Petroleum were doing business with Baghdad — for American firms, their first major involvement in Iraq.

But it wasn't long before there was infighting among Iraq's new rulers. In 1968, after yet another coup, the Baathist general Ahmed Hassan al-Bakr seized control, bringing to the threshold of power his kinsman, Saddam Hussein. Again, this coup, amid more factional violence, came with C.I.A. backing. Serving on the staff of the National Security Council under Lyndon Johnson and Richard Nixon in the late 1960's, I often heard C.I.A. officers — including Archibald Roosevelt, grandson of Theodore Roosevelt and a ranking C.I.A. official for the Near East and Africa at the time — speak openly about their close relations with the Iraqi Baathists.

This history is known to many in the Middle East and Europe, though few Americans are acquainted with it, much less understand it. Yet these interventions help explain why United States policy is viewed with some cynicism abroad. George W. Bush is not the first American president to seek regime change in Iraq. Mr. Bush and his advisers are following a familiar pattern.

The Kassem episode raises questions about the war at hand. In the last half century, regime change in Iraq has been accompanied by bloody reprisals. How fierce, then, may be the resistance of hundreds of officers, scientists and others identified with Saddam Hussein's long rule? Why should they believe America and its latest Iraqi clients will act more wisely, or less vengefully, now than in the past?

If a new war in Iraq seems fraught with danger and uncertainty, just wait for the peace.

Roger Morris, author of "Richard Milhous Nixon: The Rise of an American Politician," is completing a book about United States covert policy in Central and South Asia.