Obama Warns Terrorists: 'ISIL Is Going to Lose'

President Obama formally unveiled his request for legal authorization to fight ISIS in Iraq and Syria, declaring that the ongoing military campaign will succeed in destroying the extremist group.

"Make no mistake this is a difficult mission, and it will remain difficult for some time," Obama said in a televised statement from the White House, "but our coalition is on the offensive and ISIL is on the defensive."

"ISIL is going to lose," he said, flanked by Vice President Joe Biden, Secretary of State John Kerry and outgoing Defense Secretary Chuck Hagel.

Obama said the draft war-powers request would "strike the necessary balance" and give him "flexibility" to defeat the militants. But he sought to reassure Americans "it is not the authorization of another ground war like Afghanistan or Iraq."

While the U.S.-led war against ISIS, also referred to as ISIL, has been underway since August, Obama has sought formal endorsement from Congress to "show the world we are united in our resolve."

The three-page draft war powers resolution sent to Capitol Hill today declares ISIS a "grave threat" to the national security of the U.S. and its allies. It notes the terror group's intention to conduct attacks around the globe and a record of "despicable acts of violence," including the murder of four U.S. citizens -- James Foley, Steven Sotloff, Peter Kassig and Kayla Mueller.

Obama proposes that Congress authorize a military campaign against ISIS for three years, without restrictions on geographic scope. He also wants potential future deployment of U.S. ground combat forces to remain on the table, though the resolution would rule out "enduring offensive ground combat operations."

In a letter to lawmakers, Obama explained that he wants to retain "flexibility" in the fight, even as he publicly pledges no long-term, large-scale ground war as the U.S. led in Iraq and Afghanistan.

He cited rescue operations, special operations raids, intelligence collection and the need for ground controllers to help guide airstrikes as the limited scenarios that could require U.S. military personnel.

The president also requested cancellation of the 2002 measure authorizing the Iraq War, but does not address the 2001 authorization for the campaign in Afghanistan.

Lawmakers on both sides of the aisle reacted cautiously to terms of the president's request. Many Democrats have expressed concern that the authorization is too broad, while many Republicans have complained it may be too narrow.

"The delivery of this authorization is the beginning of a legislative process that will involve hearings, markups and I'm sure changes as we go through this process," House Speaker John Boehner said at a news conference. "I believe that if we're going to authorize the use of military force, the president should have all the tools necessary to win the fight that we're in."

House Democratic leader Rep. Nancy Pelosi stopped short of endorsing Obama's proposal, saying in a statement that lawmakers should ensure that whatever is voted upon should be "narrowly tailored" to the fight against ISIS.

If and when Congress will vote on a compromise resolution remains unclear. It would be the first war vote in Congress in 13 years, with major implications for coming political campaigns.

ABC News' John Parkinson contributed to this report.