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Washington (CNN) -- President Obama will announce the U.S. troop strategy for Afghanistan in a speech at 8 p.m. ET Tuesday at the U.S. Military Academy at West Point, New York, White House spokesman Robert Gibbs said Wednesday.
In the speech, Obama will explain why the United States is in Afghanistan, its interests there and his decision-making process, Gibbs said, but "the president does not see this as an open-ended engagement.
"Our time there will be limited, and I think that's important for people to understand," he said.
"We are in year nine" in Afghanistan, Gibbs told reporters. "We're not going to be there another eight or nine years."
Obama will meet with members of Congress at the White House on Tuesday afternoon before the speech.
Cost issues are among the topics the president will address, Gibbs said.
"It's a million dollars a troop for a year," he said. "Ten thousand troops is $10 billion. That's in addition to what we already spend in Afghanistan and Pakistan. That also does not include training, and it doesn't include the maintaining of a security force. It's very, very, very expensive."
But, Gibbs added, "I think the president, throughout this process, has talked about the cost in terms of American lives and in terms of the cost to our treasury, and I think he'll continue to talk about it."
The president ordered more than 20,000 additional troops to Afghanistan in March. Gen. Stanley McChrystal, the U.S. commander in Afghanistan, reportedly has called for up to 40,000 more to wage a counterinsurgency campaign against the Taliban, the Islamic militia originally ousted by U.S. military action in 2001.
Obama has weighed several options for bolstering the American contingent, ranging from sending a few thousand troops to the 40,000 McChrystal requested.
A defense official told CNN earlier this week the Pentagon is making detailed plans to send about 34,000 more troops to Afghanistan in anticipation of Obama's decision on the 8-year-old war.
There had been no final word on Obama's decision as of Tuesday, said the Defense Department official, who has direct knowledge of the process. But the official said planners have been tasked with preparing to send 34,000 additional American troops to Afghanistan with the expectation that Obama was leaning toward approving that many.
Defense Secretary Robert Gates is expected to receive the paperwork Thursday to approve orders to deploy 1,000 Marines from Camp Lejeune, North Carolina, to Afghanistan in late December -- the first of the new troops to be sent, a U.S. military official told CNN on Wednesday. The official is not authorized to talk about the plans because they have not been officially announced.
The 1,000 Marines are part of a battalion task force that has been preparing and training for the deployment, the official said.
The president held a lengthy meeting with top advisers Monday night, and he told reporters Tuesday that he would announce new plans for Afghanistan after Thanksgiving.
McChrystal took part in the meeting Monday, along with Vice President Joe Biden, Gates, Joint Chiefs of Staff Chairman Adm. Michael Mullen and Karl Eikenberry, the U.S. ambassador in Kabul, Afghanistan.
Obama said Tuesday that the deliberations had been "comprehensive and extremely useful."
"It's going to be important to recognize that in order for us to succeed there [in Afghanistan], you've got to have a comprehensive strategy that includes civilian and diplomatic efforts," he said at a news conference Tuesday with visiting Indian Prime Minister Manmohan Singh.
The defense official said Tuesday that the military is planning to send three U.S. Army brigades, totaling about 15,000 troops; a Marine brigade with about 8,000 troops; a headquarters element of about 7,000; and between 4,000 and 5,000 support troops -- a total of about 34,000 troops. CNN reported last month that this was the Pentagon's preferred option.
However, the official said Wednesday that the Marines are expected to deploy 8,000 combat, aviation and support troops, plus 1,000 to 1,500 Marines as part of a headquarters unit -- a total of between 9,000 and 9,500. They will be in addition to the 11,000 Marines already in Afghanistan. After the first deployment, the remaining Marines will deploy over the next three to four months, the military official said.
The troops would be dispatched throughout Afghanistan but would be focused mainly on the southern and southeastern provinces, where much of the recent fighting has taken place. Currently, brigades from Fort Drum in upstate New York and Fort Campbell in Kentucky are among those next in line to deploy.
About 68,000 U.S. troops are in Afghanistan, along with about 45,000 from the NATO alliance.
Two U.S. military officials have told CNN that NATO countries would be asked to contribute more troops to fill the gap between the 34,000 the Pentagon expects Obama to send and the 40,000 McChrystal wants. The request is expected to come during a December 7 meeting at the alliance's headquarters in Brussels, Belgium.
Secretary of State Hillary Clinton will travel to Brussels next week to meet with allies, State Department sources told CNN.
Pentagon spokesman Geoff Morrell would not discuss specific numbers, but he said NATO would be asked for additional help.
Obama's Afghanistan plan will include "very broad terms" that show how and where the United States is succeeding in the nation, a senior U.S. military official told CNN. Those points will be used to determine how and when troops can be brought home.
Another senior military official said McChrystal will take his orders from Obama and will do the best he can with what he has.
The question, he said, is not the number of troops, but is whether the United States has "the right resources to do what we need to do."
"We can't just go and blow people up and win this war," the official said. "We have to gain the trust of the people, and that is a major part of the plan here."
U.S.-led troops invaded Afghanistan in response to the al Qaeda terrorist network's September 11, 2001, attacks on New York and Washington. The invasion overthrew the ruling Taliban, which had allowed al Qaeda to operate from its territory -- but most of the top al Qaeda and Taliban leadership escaped the onslaught.
Taliban fighters have since regrouped to the mountainous region along Afghanistan's border with Pakistan, battling U.S. and Afghan government forces on one side and Pakistani troops on the other. Al Qaeda's top leaders, Osama bin Laden and Ayman al-Zawahiri, remain at large and are suspected to be hiding in the same region.
The conflict has so far claimed the lives of more than 900 Americans and nearly 600 allied troops.
CNN's Jill Dougherty, Deirdre Walsh, Elaine Quijano and Mike Mount contributed to this report.