Washington ? After months of debate, President Barack Obama will spell out a costly Afghanistan war expansion to a skeptical public tonight, coupling an infusion of as many as 35,000 more troops with a vow that there will be no endless U.S. commitment. His first orders have already been made: at least one group of Marines who will be in place by Christmas.

Obama has said that he prefers “not to hand off anything to the next president” and that his strategy will “put us on a path toward ending the war.” But he doesn’t plan to give any more exact timetable than that tonight.

The president will end his 92-day review of the war with a nationally broadcast address in which he will lay out his revamped strategy from the U.S. Military Academy at West Point, N.Y. He spent part of Monday briefing foreign allies in a series of private meetings and phone calls.

Before Obama’s call to Britain’s Gordon Brown, the prime minister announced that 500 more U.K. troops would arrive in southern Afghanistan next month — making a British total of about 10,000 in the country. And French President Nicolas Sarkozy, whose nation has more than 3,000 in Afghanistan, said French troops would stay “as long as necessary” to stabilize the country.

Obama’s war escalation includes sending 30,000 to 35,000 more American forces into Afghanistan in a graduated deployment over the next year, on top of the 71,000 already there. There also will be a fresh focus on training Afghan forces to take over the fight and allow the Americans to leave.

He also will deliver a deeper explanation of why he believes the U.S. must continue to fight more than eight years after the war was started following the Sept. 11 attacks by al-Qaida terrorists based in Afghanistan. He will emphasize that Afghan security forces need more time, more schooling and more U.S. combat backup to be up to the job on their own, and he will make tougher demands on the governments of Pakistan as well as Afghanistan.

“This is not an open-ended commitment,” White House press secretary Robert Gibbs said. “We are there to partner with the Afghans, 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.”

On a few of the bigger questions most on the minds of increasingly restive members of Congress and the public, such as how much the additional $30 billion to $35 billion cost will balloon the already skyrocketed federal deficit, how long the U.S. commitment will continue and how it will wind down, Obama was expected to make references without offering specifics.