KABUL, Afghanistan - The military may not finish its surge of 30,000 American troops to Afghanistan until nearly a year from now, a senior U.S. commander said yesterday - a slower pace than President Obama has described.

The White House insisted it was sticking with a goal of completing the buildup by late summer.

The reinforcements begin arriving next week, and the bulk of the troops are scheduled to be in Afghanistan by summer's end. But it will probably be nine to 11 months before all the troops are in place, Lt. Gen. David Rodriguez said.

The timing is important. The sooner the full complement of 30,000 can get there, the sooner the added firepower might affect the war's direction and create conditions that would allow the Pentagon to proceed with Obama's promise to begin withdrawing troops in July 2011.

"We're still working the speed at which they can come in, and so we'll see how much faster that they can come in," said Rodriguez, the second-highest U.S. commander in Afghanistan.

Military officials had been hinting in recent weeks that the escalation might take slightly longer than the summer goal, suggesting that the administration's announcement of such a rapid escalation might not be entirely firm. Rodriguez's comments set off a flurry of reactions both at the White House and the Pentagon.

White House spokesman Robert Gibbs said Obama still "believes we should get our troops in there by the end of the summer."

Several defense officials provided a similar timeline, saying Defense Secretary Robert M. Gates has indicated that all the troops should be in place by summer's end.

Pentagon spokesman Geoff Morrell said Gates had made clear that the majority of U.S. forces were slated for arrival by midsummer and the rest by the end of summer. "That is going to be a real challenge logistically, but we are determined to meet it," he said.

The sticking point appears to involve how quickly the military can deploy a final brigade of troops - containing 4,000 to 5,000 soldiers, officials said. Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, told Congress last week that 20,000 to 25,000 troops could be in place by the end of summer. Mullen arrived in Afghanistan yesterday for a check on preparations for the new forces.

Rodriguez said the calendar for adding forces was tied to the logistical challenges the military faces in bringing in so many forces so quickly. It is a complex effort to arrange for the barracks, equipment, and tons of other supplies that enable incoming soldiers and Marines to perform their mission. Some will move to Afghanistan from the United States; some materiel will be shifted from Iraq or Kuwait.

Also, Afghanistan is landlocked and lacks the more extensive network of highways that proved valuable in the 2007 Iraq buildup.

The rapid influx is a central part of the plan to take total U.S. forces in Afghanistan to 100,000 next year, Rodriguez said, and there is a heavy focus on finding ways to speed the deployment.

"It's a lot of things that have to line up perfectly . . . to get where we want to go as fast as we want," Rodriguez said. "So it'll be plus or minus a month or two."

The calendar Rodriguez suggested is close to the one his boss, Gen. Stanley McChrystal, proposed months ago during the long deliberations about how to expand forces to take on a resurgent Taliban. Obama wanted to speed up the process as much as possible in part to send a signal of U.S. resolve.