WASHINGTON  Advisers to President Obama are preparing three options for escalating the war effort in Afghanistan, all of them calling for more American troops, as he moves closer to a decision on the way forward in the eight-year-old war, officials said Saturday.

The options include Gen. Stanley A. McChrystal’s request for roughly another 40,000 troops; a middle scenario sending about 30,000 more troops; and a lower alternative involving 20,000 to 25,000 reinforcements, according to the officials, who insisted on anonymity to discuss internal deliberations. Officials hope to present the options to Mr. Obama this week before he leaves on a trip to Asia.

While some civilian and military officials believe Mr. Obama is seeking a middle ground in the debate over Afghanistan, aides denied he has made any decision or is leaning toward any of the options. Still, Defense Secretary Robert M. Gates appears to be supportive of the middle option, some officials said, and his view is thought to be pivotal because of Mr. Obama’s respect for him and his status as a holdover from a Republican administration.

The three options define the contours of a debate that has played out in public for more than two months. General McChrystal, the top American and allied commander in Afghanistan, and his advocates argue the war cannot be won without a major infusion of forces to protect the population and ultimately turn it against the Taliban. Vice President Joseph R. Biden Jr. and others oppose a buildup in a war they believe cannot be won through conventional means and that diverts attention from Pakistan, where Al Qaeda is primarily located. There are currently 68,000 American troops in Afghanistan.