Arguments for and against the U.S. troop presence in Iraq assume that having an "exit strategy" is a fundamental military principle. It isn't. Defense Secretary Donald Rumsfeld was right in April to say, "We don't have an exit strategy, we have a victory strategy."

Yet with public support here waning and suicide attacks in Iraq persisting, the calls for an exit strategy are being heard not just in the news media, but also in the halls of Congress.

As for rhetoric, "exit strategy" didn't appear in any major U.S. publication before 1980. That was seven years after American forces left Vietnam, an exit that could hardly be called strategic, let alone triumphant. It was a business term, coined by the CEO of Docutel Corp. (which invented the ATM) in a story in The New York Times on June 4, 1980. A LexisNexis search identifies the phrase in only 17 newspaper articles during the 1980s, all business stories.

Not until 1993 was "exit strategy" used in a military context. During testimony before the Senate Appropriations Committee on April 27, 1993, Secretary of State Warren Christopher listed the Clinton administration's four conditions for military engagements, concluding, "an 'exit strategy' for getting out quickly must exist." This new approach was part of Christopher's justification for intervening in Bosnia. A writer for The Boston Globe warned that the exit strategy would take a century. And in one sense, such critics were right - 951 troops remain deployed in Bosnia today. The troops have not exited, but the genocide did.

The obvious lesson is that exit strategies are superfluous to strategy, yet pundits conceive of them as inviolate. Syndicated columnist Molly Ivins wrote twice on the topic in the months before 9/11 - claiming the 37,000 GIs in South Korea were a useless leftover from the 1950s conflict, remaining only because "we didn't have an exit strategy at the time, and no one has thought one up since." In another column, Ivins asserted that one of the two big lessons from Vietnam is "have an exit strategy."

That's pure revisionism.

The notion of planning (that is, controlling) a war is a fantasy, and timing an orderly disengagement from an active enemy is worse than fantasy. These aren't football games with clearly defined teammates, referees and an official clock.

A review of U.S. military engagements is useful here. American soldiers were deployed to Germany and Japan as occupiers after World War II. But the threat of tyranny did not fade after 1945, and the Cold War demanded America's engagement. Six decades on, troops remain widely deployed.

Pentagon data reveal that 29 countries today host more than 100 American soldiers. In all, 387,463 troops were stationed abroad last year, which is actually lower than any year from 1950 to 1992. On average, 22% of U.S. troops serve overseas, which makes 2005 relatively normal. The successful strategy of the past 50 years has been engagement and alliance, not exit and pacifism.

The pattern shows that exits are the result of failure, not success. Today, no U.S. forces are in Vietnam, where the communists invaded and conquered our ally in the South. Ask yourself: Which country is better off, the Vietnam that got an exit or the Korea that didn't?

Despite the evidence of history, politicians such as Sen. Edward Kennedy, D-Mass., see the U.S. military presence in Iraq as "part of the problem." The New Republic has said "the United States should pack up and come home," once Iraqi forces have been trained. But that's exactly the question: When will Iraq be ready to defend itself?

Patience erodes when bloodshed seems constant. But my research confirms that the enduring presence of U.S. troops enhances economic growth among host countries. Indeed, countries with high U.S. troop presence during 1950-2000 saw their economies grow nearly twice as fast as the world average. Such growth is essential now to cutting the roots of terrorism.

But don't confuse this as an argument for maintaining military forces on foreign soil ad infinitum. The argument is that the United States should do whatever is necessary to preserve peace and to promote liberty. Those are the ends. Exits and entries are the means.

Tim Kane is a research fellow in the Center for Data Analysis at The Heritage Foundation. He is a veteran Air Force intelligence officer, and former San Diego software entrepreneur.