Defense Department officials say that Iraq's defenses consist of fortified fighting positions, including dug-in emplacements for tanks and other heavy equipment. Iraq is not constructing long defensive lines or trenches as it did during the 1991 war. This appears to be part of Iraq's plan to ride out the American and allied airstrikes.

Having experienced 43 days of bombing leading up to the 1991 gulf war and four days of day and night bombing during the 1998 campaign ordered by the Clinton administration, Iraqi forces have considerable experience with American air power. Because of that, Iraq has dispersed its tanks and other heavy weapons. Some military equipment is also positioned near schools and mosques in an effort to shield them from attack.

Iraq's strategy seems to be to absorb the initial round of American airstrikes and then rush its forces to their fighting positions outside Baghdad before allied forces arrive. In terms of air defense, many batteries of antiaircraft artillery have been placed in Baghdad. The Iraqi military is constantly moving its mobile surface-to-air missile systems in an effort to elude American attack.

Fighting in the Streets

A central question, however, is whether Mr. Hussein will pull the Republican Guard divisions inside Baghdad as the Americans and their allies close in. Traditionally, only the Special Republican Guard and Iraq's intelligence and security services are allowed inside the capital, a precaution against coup attempts.

"To fight effectively in the city, he will have to pull important elements of the Republican Guard inside," a defense official said. "But he will be extremely reluctant to do so until the last moment, since they can be as much a threat to him."

Perhaps the main factor is not the number of Iraqi troops nor their specific tactics: it may come down to the Iraqi military's will to fight against a technologically superior and better trained adversary. American intelligence officials believe that the morale of Iraq's regular army forces is low and on the decline. Even the morale of some Republican Guard units is suffering, officials say.

Much will depend on whether Iraq's generals conclude that Mr. Hussein is going to fall, on how they assess their chances of surviving the fighting, and on what place they might secure in a postwar Iraq.

"We expect some resistance from the Republican Guard," a Defense Department official said. "From the regular army, we expect very little."