The dimming outlook for significant U.S. troop cuts in Iraq means the Pentagon may soon face a difficult and politically sensitive decision: either make more frequent call-ups of some National Guard and Reserve troops or expand still further the size of the active-duty Army, defense officials say.

That choice, already under discussion but with no timetable for decision, is looming in light of the fact that the simultaneous wars in Iraq and Afghanistan have put the Army under enormous strain. In particular, active-duty soldiers are not getting the desired minimum of two years at home between combat deployments.

Army officials had hoped for some troop relief in Iraq in this election year, but the surge in sectarian violence, the persistence of the insurgency and the slow pace of political progress in Baghdad have snuffed out those hopes.

Gen. John Abizaid, the commander of U.S. forces throughout the Middle East, told reporters in Washington on Tuesday that the military will likely maintain — or possibly even increase — force levels of more than 140,000 troops in Iraq through next spring. The current total is 147,000, up about 20,000 since June.

Late last year, military leaders had indicated they hoped to reduce troop levels to about 100,000 by the end of this year for an Iraq war that has become widely unpopular at home. But Abizaid said Tuesday that rising sectarian violence and slow political progress made that impossible.

"I think that this level probably will have to be sustained through the spring," he said. "I think that we'll do whatever we have to do to stabilize Iraq and Afghanistan and use the military power of the U.S. to do that."

The U.S. military has about 21,000 troops in Afghanistan, an increase of several thousand over the past year.

Abizaid, Defense Secretary Donald H. Rumsfeld and Joint Chiefs of Staff Chairman Gen. Peter Pace are expected to meet with members of Congress later this week.

President Bush, in New York for U.N. General Assembly meetings on Tuesday, told Iraqi President Jalal Talabani that the U.S. will keep soldiers in Iraq as long as necessary. "I've told the president of Iraq that America has given her word to help you and we will keep our word. The people of Iraq must know that," Bush said.

Meanwhile, the White House denied reports that American officials are beginning to question whether Prime Minister Nouri al-Maliki can hold Iraq together and take the steps necessary to end its sectarian troubles.

"It's absolutely false," White House press secretary Tony Snow said. "The man has been in power for barely more than 100 days, and frankly there has been significant progress."

The Army has been aiming to reorganize its combat forces in such a way as to increase the number of brigades available for deployments to Iraq and Afghanistan, but thus far it is six brigades short of its goal of 42. That is one reason why the Army was forced in 2004-05 to use more National Guard combat units in Iraq than normal; at one point there were seven Guard combat brigades there, compared with just one now.

But even now, active-duty Army brigades are cycling in and out of Iraq and Afghanistan at a faster pace than the goal of one year deployed for every two years at home. That puts a great deal of stress on the soldiers and their families.

"I don't know how long" that can go on, a senior defense official said in an interview this week. He spoke on condition of anonymity because of the sensitive nature of the problem, which is being discussed behind closed doors.

The official likened the earlier troop-reduction plan for Iraq to the situation facing a soldier traveling down a road with a map that does not match the terrain he's seeing: The soldier has to deal with the terrain as it actually exists.

For the U.S. military, the road in Iraq has gotten rockier rather suddenly. An indication of that was the decision to extend the yearlong tour of duty for the Army's 172nd Stryker Brigade; some of the unit's soldiers had already left Iraq — and families had already hung welcome home banners around the 172nd's main base in Alaska — when the decision to extend their tour by four months was announced in late July.

The Army has committed itself to not mobilizing National Guard and Reserve soldiers for war duty more than one year out of five. But in light of the possibility that troop requirements for Iraq and Afghanistan will remain high into 2007 and beyond, officials are already discussing whether in some cases Guard or Reserve soldiers may have to be recalled more frequently.

If it is decided to stick to the once-in-five-years formula for the Guard and Reserve, then it may be necessary to increase the size of the active-duty Army, the official said. The Army already is on a path to grow by 30,000 soldiers, to 512,000. It expects to end this fiscal year Sept. 30 at about 504,000 soldiers.

Michael O'Hanlon, a defense analyst at the Brookings Institution who closely follows developments in Iraq, said Tuesday the Army should have put itself on a course to grow beyond the 512,000 mark at the outset of the war rather than wait until now. Many in Congress pushed for a bigger increase in the Army, but Rumsfeld argued against it, in part because of the enormous long-term costs.

"We are in a dilemma," O'Hanlon said. "A radical new policy may be needed, such as offering citizenship to foreigners abroad if they'll serve first" in the U.S. military.