WASHINGTON (AP) _ Setting the stage for possible war, the United States and Britain have nearly tripled the number of air patrols in the ``no fly'' zone over southern Iraq, a senior defense official said.

The purpose: to keep Iraqi defenders off guard and mask the start of actual combat.

The increased air missions are an unmistakable sign that, while President Bush has not yet announced an intention to go to war, the Pentagon is close to having set the stage for an invasion.

White House spokesman Ari Fleischer said Wednesday that Bush has discussed with congressional leaders a timetable for deciding on war, but he said the president was not specific.

``The one timetable that the president identified that remains operative is when on Jan. 30 he said weeks, not months,'' Fleischer said.

In accordance with U.S. military doctrine, Gen. Tommy Franks, the commander of U.S. forces in the Persian Gulf, is now establishing an irregular pattern of flights over invasion routes in the south, making it more difficult for Iraqi air defenders to foresee a shift from air patrols to actual combat.

Several hundred sorties a day are now being flown over southern Iraq, including F-16 and other attack planes as well as surveillance, refueling and other support aircraft, the official said, speaking on condition of anonymity. The official did not reveal specific numbers.

The increase is meant to preserve an element of surprise for the start of a war, which is expected to unleash a barrage of bombs 10 times as great as in the opening days of the 1991 Gulf War.

Franks and Defense Secretary Donald H. Rumsfeld both said at a Pentagon news conference Wednesday that Bush has not yet decided to go to war.

Rumsfeld, Franks and other senior military and senior national security officials met with the president at the White House to go over final planning for an Iraq war. Other officials said the intent, if Bush decides war is necessary, is to launch an air assault to ``shock and awe'' Iraqi defenders.

Many of the bombs would be guided by lasers or satellite signals, adding to accuracy, one official said.

Franks said the U.S. forces now arrayed against Iraq, said to number at least 230,000 with many more on the way, are prepared for a go-ahead from Bush.

``Our troops in the field are trained, they're ready, they are capable,'' Franks said.

Secretary of State Colin Powell indicated that little time remains for Saddam Hussein to meet disarmament demands.

``We will see in the next few days whether or not he understands the situation he is in and makes that choice,'' Powell said.

As part of a psychological campaign aimed at weakening the Iraqi army and undermining support for Saddam, U.S. planes on Tuesday dropped 420,000 leaflets in southern Iraq. ``Leave now and go home,'' some leaflets said. ``Watch your children learn, grow and prosper.''

Franks said he could not estimate how many Americans might die in an Iraq war, but he expressed ``incredible confidence'' in their ability to fight and win.

Franks also declined to offer an estimate of how long a war might last, even in general terms. Many military officials have said they expect it to be shorter than the 1991 war, which began with a five-week bombing campaign followed by a decisive 100-hour ground war to liberate Kuwait.

In the 1991 war, 148 U.S. troops were killed.

Franks said that in the lead-up to that conflict, there were predictions of many U.S. casualties and few people anticipated the ground phase of the war would be so short.

``Since we can't know what the duration will be, we can't predict, using some formulation, some mathematical model, what casualties might look like,'' he said. ``And so I won't predict numbers of casualties.''