WASHINGTON (AP) — President Barack Obama asked Congress Wednesday to formally authorize military force against the Islamic State group, arguing the militants could pose a threat to the U.S. homeland if their violent power grab goes unchecked and urging lawmakers to "show the world we are united in our resolve to counter the threat."

The president elected on a promise to end America's wars is sending Congress a proposed joint resolution to authorize military force against the swift rise of Islamic State extremists, who are imposing violent rule across Iraq and Syria and have brazenly killed U.S. and allied hostages in brutal online propaganda videos.

In a five-paragraph letter to lawmakers accompanying the three-page draft resolution provided to The Associated Press, Obama said the Islamic State "poses a threat to the people and stability of Iraq, Syria and the broader Middle East and to U.S. national security."

"It threatens American personnel and facilities located in the region and is responsible for the deaths of U.S. citizens James Foley, Steven Sotloff, Abdul-Rahman Peter Kassig, and Kayla Mueller," he said, listing the American hostages who died in IS custody. "If left unchecked, ISIL will pose a threat beyond the Middle East, including to the United States homeland."

Obama plans to speak on his request from the White House Wednesday afternoon.

Obama's proposal launches an ideological debate over what authorities and limitations the commander in chief should have in pursuit of the extremists, with the shadow of lost American lives hanging over its fate. Confirmation of the death of 26-year-old humanitarian worker Mueller on the eve of Obama's proposal added new urgency, while the costly long-running wars in Iraq and Afghanistan were a caution to some lawmakers against yet another protracted military campaign.

Obama is offering to limit authorization to three years, extending to the next president the powers and the debate over renewal for what he envisions as a long-range battle. He is proposing no geographic limitations where U.S. forces could pursue the elusive militants. The authorization covers the Islamic State and "associated persons or forces," defined as those fighting on behalf of or alongside IS "or any closely-related successor entity in hostilities against the United States or its coalition partners."

Obama's resolution would repeal a 2002 authorization for force in Iraq but maintain a 2001 authorization against al-Qaida in Afghanistan, although Obama said in his letter to lawmakers his goal is to refine and ultimately repeal that authorization as well.

Obama's proposal bans "enduring offensive combat operations," a novel term in military force authorizations. Its ambiguity is designed to bridge the divide between lawmakers opposed to ground troops and those who say the commander in chief should maintain the option.

Obama said his draft would not authorize long-term, large-scale ground combat operations like those deployed in the past to Iraq and Afghanistan, arguing those battles should be left to local forces instead of the U.S. military.

"The authorization I propose would provide the flexibility to conduct ground combat operations in other more limited circumstances, such as rescue operations involving U.S. or coalition personnel or the use of special operations forces to take military action against ISIL leadership," Obama said, using an acronym for the group. "It would also authorize the use of U.S. forces in situations where ground combat operations are not expected or intended, such as intelligence collection and sharing, missions to enable kinetic strikes or the provision of operational planning and other forms of advice and assistance to partner forces."

Tennessee Sen. Bob Corker, the chairman of the Senate Foreign Relations Committee, said he appreciated the president seeking the authorization and would quickly begin holding "rigorous hearings" on the White House request.

"Voting to authorize the use of military force is one of the most important actions Congress can take, and while there will be differences, it is my hope that we will fulfill our constitutional responsibility, and in a bipartisan way, pass an authorization that allows us to confront this serious threat," Corker said.

White House press secretary Josh Earnest said the provision would allow special operations missions, such as potential raids targeting Islamic State leaders and the failed attempt last summer to rescue the 26-year-old Mueller and other hostages held by the group. "It's impossible to envision every scenario where ground combat troops might be necessary," Earnest said in the White House's first interview laying out its case for the resolution.

"The president believes this sort of strikes the right balance of enforcing what he has indicated is our policy, while preserving the ability to make some adjustments as necessary," Earnest told The Associated Press.

Obama's draft resolution opens with a list of declarations against the Islamic State's "depraved, violent, and oppressive ideology," including its seizure of significant territory in Iraq and Syria, its intention and capability to expand its reach, mass killings of Muslims who don't subscribe to its beliefs, genocide against other religious groups and violence against women.

Obama argues the congressional authorizations President George W. Bush used to justify military action after 9/11 are sufficient for him to deploy more than 2,700 U.S. troops to train and assist Iraqi security forces and conduct ongoing airstrikes against targets in Iraq and Syria. Critics have said Obama is overstepping outdated authorities to target the new threat from militants imposing a violent form of Sharia law in pursuit of the establishment of an Islamic state.

Obama cast the vote as an important message to America's allies and enemies. "I can think of no better way for the Congress to join me in supporting our nation's security than by enacting this legislation, which would show the world we are united in our resolve to counter the threat posed by ISIL," he wrote to lawmakers.

Presidential aides have consulted privately with lawmakers from both parties ahead of unveiling the plan publicly in hopes of lining up support, despite the political divisions that have deadlocked Washington in Obama's second term. In anticipation of debate and attempts to amend the resolution, Earnest called the offer a "starting point for conversations to take place."

Earnest said the language limiting ground troops was designed not just for domestic political considerations, but to take in the viewpoint of leaders in Iraq and members of the U.S.-Arab coalition targeting IS uncomfortable with the idea of a large deployment of U.S. forces. He also said the lack of geographic limitations will allow pursuit of the extremists beyond the borders of Iraq and Syria. "We wouldn't want to leave them with the impression that they could go somewhere else to get a safe haven," he said.

Earnest also argued the three-year window would give the military time to carry out its strategy before Congress starts debating a renewal. The spokesman said the White House hoped the authorization would serve as a model for the next president and a new Congress when that time comes.

"The language in here should not be construed as a belief by the president that we'll have defeated and ultimately destroyed ISIL in three years," Earnest said.