WASHINGTON — President Barack Obama said Wednesday night that he was ordering a significantly expanded military campaign against Sunni militants in the Middle East that includes American airstrikes in Syria and the deployment of 475 more military advisers to Iraq. But he sought to dispel fears that the United States was embarking on a repeat of the wars in Iraq and Afghanistan.
In a televised speech from the State Floor of the White House, Obama said the United States was recruiting a global coalition to "degrade and ultimately destroy" the militants, from the Islamic State in Iraq and Syria. He warned that the effort would require years of sustained effort.
"We will hunt down terrorists who threaten our country, wherever they are," Obama said. "That means I will not hesitate to take action against ISIL in Syria, as well as Iraq. This is a core principle of my presidency: If you threaten America, you will find no safe haven." ISIL is an alternative name for the Islamic State.
The president took pains to distinguish between the military action he was putting in motion and the two wars begun by his predecessor, President George W. Bush. He likened this campaign to the targeted airstrikes that the United States has carried out for several years against suspected terrorists in Yemen and Somalia, few of them ever made public.
After enduring harsh criticism for saying in a news conference two weeks ago that he did not have a strategy for dealing with the Islamic State in Syria, Obama sketched out a plan that will involve heightened American training and arming of moderate Syrian rebels to fight the militants. Saudi Arabia has agreed to provide bases for the training of those forces.
The White House has asked Congress to authorize the plan to train and equip rebels - something the CIA has been doing covertly and on a much smaller scale - but Obama said he already had the authority necessary to expand the broader campaign.
"These American forces will not have a combat mission - we will not get dragged into another ground war in Iraq," Obama pledged, adding that the broader mission he was outlining for American military forces "will be different from the wars in Iraq and Afghanistan; it will not involve American combat troops fighting on foreign soil."
For all his efforts to reassure the public, Obama's remarks were a stark admission of the threat posed by the militants, whose lightning rampage through Iraq and Syria and videotaped beheading of two young Americans has reignited fears of radical terrorism.
The president's remarks, on the eve of the 13th anniversary of the Sept. 11, 2001, terrorist attacks, will thrust the United States into a civil war in Syria that he had long sought to avoid, and return the country to a significant military presence in Iraq, from which Obama withdrew the last American combat soldiers at the end of 2011.
The president's speech came after a frenzied effort to line up the support of partners worldwide to combat the Islamic State. Earlier on Wednesday, Obama called King Abdullah of Saudi Arabia to enlist his support for a plan to bolster the training and equipping of moderate Syrian rebels.
"The president and the king agreed on the need for increased training and equipping of the moderate Syrian opposition," the White House said in an unusually extensive briefing for reporters about the call. "President Obama welcomed Saudi Arabia's support for this program."
Obama is acting against a backdrop of rapidly shifting public opinion as polls show that a large majority of Americans now favor military action against the Islamic State group, even as they express deep misgivings about the president's leadership on the world stage.
Obama is also facing political challenges on Capitol Hill, where Republicans lawmakers, initially reluctant to demand congressional authorization of military action, have begun agitating for a vote at the same time that some Democrats are warning of a stampede to war.
But Senate Democratic leaders on Wednesday prepared legislation to expressly authorize the U.S. military to train Syrian rebels. House Republicans appeared ready to follow their lead.
Rep. Kevin McCarthy of California, the House majority leader, abruptly called off a vote on a stopgap spending bill that was planned for Thursday to reconsider Obama's request that language be included authorizing the training of the rebels. The president called the chairman of the House Appropriations Committee, Rep. Harold Rogers of Kentucky, to plead his case.
The flurry of activity means that Congress is likely to weigh in on the looming military action before the midterm elections in eight weeks. House Republicans have called an emergency meeting for Thursday morning to discuss their options, and leaders are leaning toward a vote to express some support for a broader campaign against the Islamic State.
The political atmosphere on Capitol Hill was further roiled by the sudden reappearance of former Vice President Dick Cheney, who implored Republicans to support military action and attributed the chaos in Iraq to what he called an "arbitrary and hasty" withdrawal in 2011 by Obama.
Sen. Richard J. Durbin, D-Ill., and a close political ally of Obama, rejected Cheney's critique as an unwelcome echo of the Iraq war, saying, "I think we want to be careful that we don't engage ourselves for a long period of time in a long-term war involving the vulnerability of our troops for a long period of time."
For Obama, the speech amounts to a strategy for a problem he has long said would defy an American remedy: sectarian strife between Sunni and Shiite Muslims in neighboring countries with deeply disaffected minorities and no history of democratic governance.
Among the difficult challenges to the strategy: How will the United States and its allies reinvigorate a moderate Syrian opposition that has been fractured, depleted and marginalized by more extremist forces? How can the United States act against the Islamic State in Syria without benefiting President Bashar Assad, who is also at war with the militants?
Perhaps most difficult, how can the United States wage a lengthy military campaign against a Sunni militant organization without stirring up new terrorist threats in this volatile region?
Obama's remarks were unlikely to allay those concerns, warning that the United States was embarking on a long-term campaign of heightened military activity.
Sen. Harry Reid of Nevada, the majority leader, embraced Obama's plan for military training on Wednesday, even as he expressed strong opposition to deploying U.S. ground troops.
"It's clear to me that we need to train and equip Syrian rebels and other groups in the Middle East that need some help," Reid said. "The president has tried to get that from us, and we should give it to them."
The prospect of expanding the war on the Islamic State had already become political fodder before the president's speech. Sen. Mitch McConnell of Kentucky, the Republican leader, denounced what he called Obama's weak and failed foreign policy. But he will be hard-pressed to oppose the pending vote, which could come as soon as this week.
"The president has now declared that defeating ISIL is his objective," McConnell said. "That's a good start. But Americans don't want a lecture. They want a plan - a credible, comprehensive plan to deal with this menace that clearly wants to harm us here at home, and that is only becoming stronger."