WASHINGTON - The White House said President Barack Obama could use an unusual evening war council session Monday to lock in his long-awaited decision on whether to commit tens of thousands of new U.S. forces to the stalemated war in Afghanistan.

Military officials and others said they expected Obama to settle on a middle-ground option that would deploy an eventual 32,000 to 35,000 U.S. forces to the 8-year-old conflict.

That rough figure has stood as the most likely option since before Obama's last large war council meeting this month, when he tasked military planners to rearrange the timing and makeup of some of the deployments.

The president has said with increasing frequency in recent days that a big piece of the rethinking of options that he ordered had to do with building an exit strategy into the announcement, revising the options presented to him to clarify when U.S. troops would turn over responsibility to the Afghan government and under what conditions.

As White House press secretary Robert Gibbs put it to reporters on Monday, it is "not just how we get people there, but what's the strategy for getting them out."

Obama was holding the 10th meeting of his Afghanistan strategy review since mid-September on Monday night, with a large cast of foreign policy advisers, to go over that revised information from war planners.

In the 90-minute session in the Situation Room, "they'll go through some of the questions that the president had, some additional answers to what he'd asked for, and have a discussion about that," Gibbs said.

The meeting was arranged for the unusual nighttime slot to accommodate both Obama's packed public schedule on Monday and the fact that many of his top advisers were leaving town for the holiday. No more war council meetings are on the calendar.

The presidential spokesman said it was possible Obama could lock in a decision at Monday's meeting or that it could come "over the course of the next several days." In either case, it will not be announced this week, he said.

The force infusion expected by the military would represent most but not all the troops requested by Obama's war commander, for a retailored war plan that blends elements of Gen. Stanley McChrystal's counterterror strategy with tactics more closely associated with the CIA's unacknowledged war to hunt down terrorists across the border in Pakistan.

McChrystal presented options ranging from about 10,000 to about 80,000 forces, and told Obama he preferred an addition of about 40,000 atop the record 68,000 in Afghanistan now, officials have said.

Obama already has ordered a significant expansion of 21,000 troops since taking office. The war has worsened on his watch, and public support has dropped as the number of U.S. combat deaths has increased.

The additional troops would be concentrated in the south and east of Afghanistan, the areas where the United States has most of its forces, military officials said. The new troops that already went this year were directed to help relieve Marines stretched to the limit by far-flung postings in Helmand province and that would continue, while the U.S. effort would expand somewhat in Kandahar.

The increase would include at least three Army brigades and a single, larger Marine Corps contingent, officials said.

All officials spoke on condition of anonymity because the decision was not final.

U.S. war planners would be forgoing the option of increasing U.S. fighting power in the north, a once-quiet quadrant where insurgents have grown in strength and number in the past year. But McChrystal's recommendation did not specify a quick infusion there.

Without large additions of ground forces, dealing with the north probably would require relying more heavily on air power, two military officials said. Any such additional air strikes would be more successful if, as U.S. officials hope, Pakistan turns up the heat on Taliban militants on its side of the border.

As originally envisioned by McChrystal, the additional U.S. troops would begin flowing in late January or after, on a deployment calendar that would be slower and more complex than that used to build up the Iraq "surge" in 2007. McChrystal's schedule for full deployment has it taking nearly two years, military officials said.

The relatively slow rollout is largely driven by logistics. It also could give the White House some leverage over Afghan President Hammed Karzai. U.S. officials note that where and how fast troops are deployed are a means to encourage fresh and more serious efforts at co-operation and clean government in Afghanistan.

The White House is aiming for an announcement by Obama by the middle of next week, after Congress returns from its Thanksgiving break.

Military officials, congressional aides and European diplomats said they expect Obama to deliver a national address laying out the revamped strategy. Said Obama in a television interview last week: "At the end of this process, I'm going to be able to present to the American people in very clear terms what exactly is at stake, what we intend to do, how we're going to succeed, how much it's going to cost, how long it's going to take."

Congressional hearings would immediately follow that address, including testimony from McChrystal.

"Gen. McChrystal will certainly be coming back to ... testify. When that is is still to be determined," based on the timing of the White House announcement, Pentagon spokesman Bryan Whitman said.

On the topic of increased costs in Afghanistan, Gibbs said that the subject of a war tax, suggested by some leading Democrats on Capitol Hill, has not come up yet in the president's extensive meetings with his war advisers.