WASHINGTON -- President Barack Obama in an address tonight will divulge details of his new Afghanistan strategy that will order an expected 30,000 to 35,000 additional soldiers and Marines to war, the largest single U.S. troop deployment since the 2003 invasion of Iraq.

But even as he dramatically escalates the war, Mr. Obama will emphasize limits on the U.S. involvement in the region, White House officials said.

The carefully crafted message, pairing a deep commitment to combat with a promise to eventually draw down, is aimed at a complex domestic and international audience with sharply differing preferences for the U.S. posture.

The White House said Mr. Obama issued orders to the military Sunday putting the new plan into effect. The contents of the instructions remained secret, and the Pentagon said Defense Secretary Robert M. Gates probably will issue the deployment orders to affected units later this week.

But the expected troop announcement is likely to surpass the 2007 Iraq troop surge, which pumped 21,500 combat troops and as many as 8,000 support personnel into zones in and around Baghdad.

In a televised address to an audience at the U.S. Military Academy at West Point at 8 p.m. EST, Mr. Obama will call on Afghanistan's government officials and security forces to make strides toward self-sufficiency while U.S. forces continue to help.

"You will hear the president discuss clearly that this is not an open-ended commitment," White House spokesman Robert Gibbs said. "This is about what has to be done so the Afghans can secure their country."

The speech, representing the Obama administration's second attempt to forge a joint strategy for Afghanistan and Pakistan, will reflect an all-encompassing view of the war that began with a U.S. invasion more than eight years ago. The speech will describe both military and civilian efforts to wind down the conflict, benchmarks for measuring progress and timetables for American involvement.

It also will mark Mr. Obama's second major escalation of the conflict this year. Shortly after taking office, he deployed an additional 21,000 troops. The U.S. force now stands at about 68,000, a number that commanders have said is insufficient to retard insurgent gains and stabilize the country.

Preparations for tonight's speech began Sunday, when the president delivered his orders to military officials and met with administration officials in the Oval Office. Later Sunday, he spoke by video conference with Gen. Stanley A. McChrystal, the top U.S. and allied commander in Afghanistan, and the U.S. ambassador there, Karl Eikenberry.

Yesterday, the president began calling world leaders to tell them of his decision and ask for their assistance. He planned to meet today with congressional leaders before traveling to West Point for his address.

Mr. Obama met yesterday with Australian Prime Minister Kevin Rudd and spoke by phone with French President Nicolas Sarkozy, Russian President Dmitry Medvedev and British Prime Minister Gordon Brown. He was also scheduled to speak with the heads of state in Afghanistan, Pakistan, China, Germany, Poland and India.

The White House said that in those calls to foreign leaders, Mr. Obama did not specify U.S. troop levels. But he sought assistance from allied countries' leaders as part of an international effort to stabilize Afghanistan and ensure that it does not fall to the control of forces friendly to al-Qaida.

Several European diplomats yesterday said NATO countries may be willing to field additional troops, although the approvals may not come immediately. Italy, Georgia and Ukraine are among the countries that may contribute more troops, in addition to the United Kingdom, which is adding 500, officials said.

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