BALTIMORE, 19 February 2004 — The most influential thinker in 20th-century American foreign policy completed his own century this week. And as George Frost Kennan quietly celebrated his 100th birthday Monday at home in Princeton, N.J., scholars were still debating whether his doctrine of containment, which guided eight US presidents through a treacherous Cold War, applies to new threats and a new global ideology as implacably hostile to the United States as Soviet communism.

“Kennan is a remarkable figure — there’s no one of comparable influence,’’ says Steven David, a political scientist at Johns Hopkins University. “It shows the power of ideas. It was a matter of his being at the right place at the right time with the right idea.’’

The time was February 1946 and the place was Moscow, where Kennan was completing a second tour as a diplomat assigned to the US Embassy. Set off by a routine inquiry from Washington, Kennan set down his thoughts on how to respond to the threat posed by the Soviet Union.

The 5,000-word missive that became known as the “Long Telegram’’ sketched ideas that Kennan would elaborate the next year in a seminal article in Foreign Affairs (under the pseudonym “X,’’ since he still worked for the State Department) and in books to follow.

Without flinching from the brutal, expansionist nature of the Soviet regime, Kennan proposed that the United States could outlast the Soviet Union and defeat it without resorting to catastrophic war. His belief that American strength and values, along with close cooperation with allies, would ultimately lead to the crumbling of the Soviet system was vindicated in 1991.

Now the United States faces different dangers, in the form of rogue states and a shadowy network of terrorists united by religious fanaticism. Is the principle of containment still relevant? Scholars are divided.

After the Sept. 11, 2001 terrorist attacks, President Bush announced a doctrine of pre-emption that broke explicitly with the idea of containment.

He invaded Afghanistan, vowed to hunt down terrorists around the world and ordered the toppling of Saddam Hussein’s regime in Iraq, calling it an intolerable threat. In a 2002 interview, Kennan expressed deep skepticism about the plan to invade Iraq. And the failure to find weapons of mass destruction there has prompted administration critics to assert that the war has only proven that containment was working in Iraq.

“I think containment is completely relevant for any potential enemy that has a return address — Iraq, Iran, North Korea,’’ says Bruce Cumings, professor of history at the University of Chicago. “We’ve been containing North Korea for half a century.’’

Cumings calls Kennan’s warnings about the Iraq war prescient. “Kennan was a member of a generation that built the postwar world system, and multilateralism was at the core,’’ Cumings said. “The Bush administration has badly damaged that system by refusing to work with allies and ignoring the views of France and Germany, which now seem to have been quite accurate.’’

But Al-Qaeda is a different story, according to both Cumings and David, of Johns Hopkins. “With terrorist groups that could strike at any time, my sense is that containment in inadequate,’’ David said.