Top military and diplomatic officials got their marching orders Sunday evening from President Obama ahead of a planned speech Tuesday in which he's expected to outline his new Afghanistan war strategy and call for about 30,000 more U.S. troops to be sent to the war zone.

At least one group of Marines will be deployed and in place by Christmas.

White House Press Secretary Robert Gibbs said Obama issued the orders during a meeting in the Oval Office Sunday, and they are now official. He still has to let Afghan President Hamid Karzai and Pakistan President Asif Ali Zardari know the plan.

Gibbs told reporters that Obama will highlight the importance of U.S. involvement in Afghanistan during his speech Tuesday night at the U.S. Military Academy at West Point, while acknowledging the costs and sacrifices associated with an escalation and stressing the importance of an exit strategy. While offering few specific details of the contents of Obama's speech, Gibbs said the goal of the president's revamped approach is to train Afghan security forces to eventually take over from the U.S.

"This is not an open-ended commitment," Gibbs said. "We are there to partner with Afghanistan, to train the Afghan national security forces, the army and the police so that they can provide security for their country and wage a battle against an unpopular insurgency in that country."

Gibbs said the president would "touch on" the budgetary impact of escalating the war but did not say whether he favors a new tax on the wealthy to pay for additional troops -- a proposal that some Democrats in Congress have backed.

Obama is expected to announce an increase of up to 35,000 more U.S. forces to defeat the Taliban-led insurgency and stabilize a weak Afghan government. The escalation, which would take place over the next year, would put more than 100,000 American troops in Afghanistan at an annual cost estimated to be about $75 billion.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff; Gen. David Petraeus, head of Central Command; Secretary of Defense Robert Gates; and Secretary of State Hillary Clinton were part of the war council meeting Sunday. The president afterward called Gen. Stanley McChrystal, the top commander in Afghanistan, and Karl Eikenberry, the U.S. ambassador to the country.

The decision capped months of deliberations over the way forward in Afghanistan. Though Obama ordered 21,000 more troops to the country shortly after taking office, McChrystal requested tens of thousands more in a late August assessment. That request triggered heated debate among Obama's top advisers over what the U.S. goals should be in Afghanistan and Pakistan.

Gibbs said Obama is discussing his decision Monday with a number of international leaders, including British Prime Minister Gordon Brown, Russian President Dmitry Medvedev and French President Nicolas Sarkozy.

Offering an exit strategy is something proponents of a stepped-up effort had hoped Obama would avoid. But opponents of more U.S. combat troops say it's critical for the Afghans to demonstrate they are able to manage their own security.

"The key here is an Afghan surge, not an American surge," Senate Armed Services Committee Chairman Carl Levin, D-Mich., said Sunday. "We cannot, by ourselves, win (the) war."

McChrystal has said he wants an overall Afghan security force of 400,000 -- 240,000 soldiers and 160,000 police officers -- by October 2013. Levin has proposed moving that date forward a year to 2012.

Getting Pakistan on board is also a key component for Obama, according to The Washington Post, which reported Monday that Obama had sent a letter to Zardari saying the U.S. planned no early withdrawal from Afghanistan and will increase its military and economic cooperation with Pakistan.

The Post, quoting unidentified administration officials, also said that Obama called for closer collaboration against extremist groups, including five named in the letter.

The letter, delivered by national security adviser James Jones, reportedly included a blunt warning that the U.S. would not tolerate support within Pakistan's military and intelligence operations of extremists fighting in Afghanistan.

Fox News' Major Garrett and The Associated Press contributed to this report.