Prudent policy makers sometimes make lists of the reasons for and against a possible course of action. President Bush and his national security team have been giving us reasons for going to war against Iraq: Mr. Bush says Saddam Hussein is “a bad guy.” What’s more, he says Saddam’s regime is part of an “axis of evil.” More precisely, he wants to acquire and may already have weapons of mass destruction. In fact, he already has used chemical warfare against Iranians and against Iraq’s Kurdish dissidents. Furthermore, Saddam may have been in cahoots with Osama bin Laden and his Islamic terrorist conspiracy, al Qaeda. But here the case gets hazy. It rests mainly on a supposed meeting, reported and denied several times of Mohammad Atta, chief of the Sept. 11 hijackers with an Iraqi diplomat in Prague five months before the September terrorist attack. The story could mean something or nothing, depending on what was said at the supposed meeting and what came of it. Former CIA Director James Woolsey, who has been called the Paul Revere of the terrorism age and is campaigning for a U.S. effort to overthrow Saddam, admits that there is no smoking gun but told Salon, the internet magazine, that establishing a Saddam-bin Laden link is unnecessary. He argues that Saddam continues to develop nuclear and biological weapons and the missiles to deliver them, so “it’s important to move against him sooner rather than later.”

So much for the pros. We hear less about the cons. Here are some to consider:

. Iraq is not Afghanistan. The campaign in Afghanistan was short and relatively easy. For Iraq, the Pentagon is thinking in terms of 200,000 U.S. troops and a year of fighting, Such estimates have a way of expanding.

. Internal revolt in Iraq is speculative at best. American hawks have high hopes for an uprising by the Iraqi National Congress, but, with its emigre leadership, it is nowhere near the home-grown Afghan Northern Alliance that was such a force in overthrowing the Taliban.

. In view of the coolness of our usual allies to the project, the United States may head into this one all alone.

. What about unforeseen consequences? Both Iraq and Turkey, the likely main staging base for a U.S. invasion, are wobbly countries with deep ethnic and tribal divisions. They could fly apart like Yugoslavia. The United States could find itself responsible for a wholesale round of nation building that would make the struggle over the remnants of Yugoslavia look like a picnic.

. Finally, what about the preemptive warfare that Mr. Bush is calling for? At West Point on June 1, he said that deterrence means nothing against terrorist networks and that, “if we wait for threats to fully materialize, we will have waited to long.” This new first-strike policy affronts the European allies who backed the United States so strongly in the Gulf War and in Afghanistan. And it can stir a question in some American hearts and minds: Why are we departing from the fine old standard of defending with all our might against attack but never starting a war.

The new policy sounds like a throwback to discredited jingoism, which got its name from the old British line, “We don’t want to fight, but by jingo if we do, we’ve got the ships, we’ve got the men, and got the money, too.”