The massive Iraqi force now entrenched in Kuwait would require weeks to withdraw completely from there, no matter when Iraqi President Saddam Hussein might decide to comply with international mandates that his entire force pull out, according to Pentagon officials and military analysts.

"It could be a matter of weeks," said Pentagon spokesman Pete Williams. "It could be a matter of months, depending upon whether all their forces are simply going to drop everything and leave in the fastest possible way or whether they're going to take equipment with them."

"It's taken him a very long time to put it there, so obviously it's going to take him a long time to get it all out," said another senior military official.

President Bush said Saturday that he believes it may not be "logistically possible to fully comply . . . if he started now."

White House Chief of Staff John H. Sununu said yesterday that Saddam "moved into Iraq in two days with his tanks and a couple of hundred thousand troops and he can move at least that much out in two days. And he ought to start."

But military authorities say the massive logistics of moving an estimated 270,000 troops out of Kuwait will complicate efforts in the first days to assess whether military activity represents serious withdrawal efforts or calculated stalling attempts.

Sununu, interviewed on CBS's "Face the Nation," said: "If it is clear that he is on the way to completion, I think the president will take that into account. . . . But the key right now is to make sure that what is done is not another ploy but truly a withdrawal in a quick, timely and effective way."

"He's already demonstrated that he's conducted fake withdrawals in the early days of the occupation," said one military skeptic. "If he wanted to prolong the withdrawal period, he has the potential to do that."

Approximately one-half of the 540,000 troops Saddam has arrayed for potential combat are inside Kuwait; the remainder are in southern Iraq in position to move south rapidly if ordered to reinforce troops in Kuwait.

Even if Iraq pulls all of its troops out of Kuwait and into Iraq, a formidable fighting force would remain massed just across the border, presenting a continuing threat to security in the region, military officials note.

"The question is, 'Do you leave Saddam Hussein and his war machine intact?' " said one military official. "If he suddenly withdraws from Kuwait and satisfies all the U.N. resolutions, you still have the problem that he could do it all over again."

Over the past five months, the Iraqi military has constructed a mammoth system of trenches, embattlements and minefields around its armor and infantry units.

"We'll need something on the order of 24 to 72 hours just to see him start to move," said one military analyst.

The U.S. military will monitor the actions of the Iraqi army with overhead satellite imagery, side-looking airborne radars that allow aircraft to "see" far into the horizon and other intelligence-gathering methods to determine which of its units are being withdrawn first.

Withdrawal efforts likely would be slowed by the tedious process of loading hundreds of tanks and armored personnel carriers onto trucks and moving them out of Kuwait.

"It is the problem of big, mechanized armies the world over, including the United States," said one Army official. "It's not practical to move tanks great overland distances under their own power. It is hell on the tracks and the roads."

Military officials said that in a serious withdrawal effort, they would expect to see some logistics and supply lines from Iraq -- particularly those for ammunition, spare parts and other military equipment -- shut down. They noted, however, that even during a withdrawal, the Iraqi forces would need to continue to send food, fuel and some other supplies to the front-line areas to support the withdrawal effort.

"The subsistence that goes into the maintenance of an army anyplace has to go on," said one Pentagon official. "You're likely to see the roads clogged with troops that are withdrawing going north and convoys bring food and gasoline for troops to the south."

Authorities say the pace of the Iraq withdrawal will depend on the extent of the dismantling of the military's massive fortifications, which have taken months to construct.

While U.S. military officials said it would be unnecessary for the Iraqis to completely disassemble the fortifications, they are extremely concerned about the vast minefields that have been laid by the troops.

"What does he do with the mines left in place?" said one congressional military analyst. "Does he get up and move out and leave them for us to clear? I would hope not."

The U.S. military already has stationed teams of demolition experts throughout the Middle East to move into Kuwait and help clear minefields after the withdrawal, whether it is conducted peacefully or as the result of war.

Officials said that in any pullout effort, Iraq likely would leave a thin screen of heavily armored forces in place near Kuwait's border with Saudi Arabia to protect withdrawing forces from potential unexpected attack.