Mr. Obama himself seems to be hedging his bets, particularly on the performance of Mr. Karzai, who is considered by American officials to be an unreliable partner and is now widely derided in the White House. Mr. Obama told ABC News during an interview on Monday that given the weakness of the Karzai government in Kabul, his administration was seeking “provincial government actors that have legitimacy in the right now.”

Officials said that while Admiral Mullen and Mrs. Clinton were generally in sync with Mr. Gates in supporting an option of about 30,000 troops, there were variations in their positions and they were not working in lock step. Admiral Mullen’s spokesman, Capt. John Kirby, said that the admiral was providing his advice to the president in private and would not comment. Geoff Morrell, the Pentagon press secretary, would not comment on Mr. Gates’s position.

A focus of Mr. Obama’s meeting on Wednesday with his national security advisers, officials said, will be to discuss some of their differences as well as those of the president’s other advisers. Officials also said there was a possibility that Mr. Obama might choose to phase in additional troops over time, with a schedule that depended on the timing of the arrival of any additional NATO troops and on how soon Afghan security forces would be able to do more on their own.

Officials said that no decision was expected from Mr. Obama on Wednesday, but that he would mull over the discussions at the meeting during a trip to Asia that begins Thursday. Mr. Obama is not due back in Washington until next Thursday. Officials said that it was possible that he could announce his decision in the three days before Thanksgiving, which is on Nov. 26, but that an announcement in the first week of December seemed more likely.

Should Mr. Obama choose to send about 30,000 troops, a military official said, brigades would most likely be sent from the 101st Airborne Division at Fort Campbell, Ky., and the 10th Mountain Division at Fort Drum, N.Y. In addition, 4,000 troops would be sent as trainers for the Afghan security forces, the military official said. A brigade is about 3,500 to 5,000 soldiers.

Senator Jack Reed, the Rhode Island Democrat who has been an influential adviser in the Afghanistan debate, said that one of the most difficult issues was determining the effects of a large American troop presence on the country.

“It’s more about, hey, are we creating such a large footprint that it’s easier for the Afghans to walk way from their responsibility?” Mr. Reed said. “I don’t think that’s one that can be resolved. You’re making a judgment about that one, and not one you can solve with arithmetic.”