Such a narrowed military mission would escalate American forces to accomplish the commander's broadest goals, protecting Afghan cities and key infrastructure. But the option's scaled-down troop numbers likely would cut back on McChrystal's ambitious objectives, amounting to what one official described as "McChrystal Light."
Analysis: On Afghanistan, a Decision Comes Slowly
Under the pared-down option, McChrystal would be given fewer forces than the 40,000 additional troops he has asked for atop the current U.S. force of 68,000, officials told The Associated Press on Wednesday.
Senior White House officials stressed, however, that the president has not settled on any new troop numbers and continues to debate other strategic approaches to the 8-year-old Afghanistan war. The officials say Obama has not yet firmly settled on the narrowed option or any other as his final choice for how to overhaul the war effort.
Two officials, speaking on condition of anonymity because Obama has not announced his decision, said the troop numbers under the narrowed scenario probably would be lower than McChrystal's preference, at least at the outset. The officials did not divulge exact numbers.
The stripped-down version of McChrystal's plan still would adopt the commander's overall goals for a counterinsurgency strategy aimed at turning the corner against the Taliban next spring.
But that pared-down approach would reflect a shift in thinking about what parts of the war mission are most important and the intense political domestic debate over Afghan policy.
A majority of Americans either oppose the war or question whether it is worth continuing to wage, according to public opinion polls dating to when Obama shook up the war's management and began a lengthy reconsideration of U.S. objectives earlier this year.
Any expansion of the war will displease some congressional Democrats. If Obama does not meet McChrystal's request, Republicans are likely to accuse Obama of failing to give McChrystal all of what he needs.
A stripped-down approach would signal caution in widening a war that is going worse this year than last despite intense U.S. attention and an additional 21,000 U.S. forces on Obama's watch.
Fourteen Americans were killed Monday in Afghanistan in two helicopter crashes, and roadside bombings Tuesday left eight U.S. troops dead. October has been the worst month for U.S. fatalities since the U.S.-led invasion of Afghanistan began in October 2001.
Even if McChrystal gets less than he wants from Obama, the U.S. may still end up adding more troops later in 2010. The most likely reason would be to fill voids left by some NATO allies who have been considering troop cutbacks.
Defense Secretary Robert Gates has pushed back hard against a faction of administration officials, led by Vice President Joe Biden, who contend that much of the U.S. national security objective in Afghanistan could be accomplished by concentrating on strikes at al Qaeda along the Pakistan border.
That approach would hunt terrorists with techniques such as missile-loaded pilotless drones, and could require little or no additional U.S. manpower.
Gates has bridged both sides, officials said. Long wary of a large U.S. presence that could too easily look like an occupation army, he has suggested recently that he could support a carefully designed expansion.
Obama meets Friday with the Joint Chiefs of Staff, the military leaders who would have the responsibility for carrying out his strategy decisions. White House officials said the president will continue to consider his options with advisers over the next couple of weeks, adding that other broad war council meetings may still be called during that period.
The White House preference is to announce the troop decision after Afghanistan's run-off presidential election on Nov. 7, but before Obama leaves for an unrelated foreign trip on Nov. 11. That timing is not assured, however, and no announcement plan has been settled upon by Obama and his aides, officials said.
Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, is on record supporting a troop increase. He has not quantified his preference, but he signed off on McChrystal's assessment of the worsening conditions in Afghanistan and the need for a change in approach and boost in manpower.
Gates has not given a public opinion on McChrystal's request but has pushed for the commander's overarching strategy during recent weeks of review by the White House, officials said.
"I think that the analytical phase is ... coming to an end," Gates said last week in Europe. "Probably over the next two or three weeks we're going to be considering specific options and teeing them up for a decision by the president."
As for McChrystal, he already begun carrying out elements of his targeted counterinsurgency plan, which focuses on the volatile south and east of the country and emphasizes protecting civilians even if it means allowing individual militants to escape.
McChrystal's recommendations got broad endorsement from NATO defense chiefs last week, with the suggestion that some nations will increase troops or other resources.
The Friday meeting is the last formal session the president has scheduled to review the situation in Afghanistan and neighboring Pakistan, a decision-making process that Republican critics say has taken too long.