The Obama administration is preparing to send Congress a proposal authorizing limited military force against the Islamic State, although it could prompt criticism from both parties.

Fox News is told that the resolution will include language urging no “enduring combat ground forces” while also not expressly prohibiting so-called “boots on the ground."

The widely varying views on the need for U.S. ground operations is part of a search for a compromise that could satisfy Democrats who oppose the use of American ground forces in the fight, and Republicans who favor at least leaving the possibility open.

Sen. Bob Menendez, D-N.J, describing the proposal to reporters, said President Obama would seek authorization for the use of force that would expire after three years. It would end the approval for operations in Iraq that Congress passed in 2002.

Menendez spoke after he and other Democratic senators met privately Tuesday with top White House aides, on the eve of an anticipated formal request for legislation from the president.

"Hopefully there will not be a significant delay in Congress acting," said White House press secretary Josh Earnest.

A sticking point is whether an authorization for the use of military force should include a so-called sunset provision, a window for which the authorization would either expire or have to be renewed. Fox News learned Tuesday evening that House Democrats had discussed a sunset provision of three years, but it was unclear whether House Republicans would agree to such a deadline.

The meetings unfolded against a fresh reminder of the threat posed by terrorists who occupy large areas of Syria and Iraq -- the confirmed death of a 26-year-old American aid worker who had been held hostage by the group.

Obama pledged to bring anyone responsible for Kayla Mueller's captivity and death to justice "no matter how long it takes."

Menendez, in describing the White House's opaque formulation, said it remained subject to modification. "That's where the rub will be," he said.

One senior Democrat, Sen. Barbara Mikulski of Maryland, said she has significant questions about the president's proposal. "I don't know what the word `enduring' means. I am very apprehensive about a vague, foggy word," she said.

Menendez also said it was not yet clear if the proposal would cancel a 2001 authorization for the use of force that Congress approved shortly after the terrorist attacks of Sept. 11, 2001.

Republicans control both houses of Congress, and presidents generally court bipartisan support for legislation of the type Obama now seeks.

Several other lawmakers who were briefed in earlier meetings, said the president would likely seek legislation targeted exclusively against the fighters seeking establishment of an Islamic state, wherever they are and whatever name they use.

Apart from the midday meeting with Democrats in the Capitol attended by White House Chief of Staff Denis McDonough, some Republicans expressed concern with other elements of the administration's emerging proposal.

Sen. Lindsay Graham, R-S.C., said administration officials had told him it would not provide for the protection of U.S.-trained Syrian rebel troops on the ground in the event of an air attack by Syrian forces loyal to President Bashar Assad.

"It's an unsound military strategy. I think it's immoral if the authorization doesn't allow for us to counter Assad's air power," he said.

There was little evident dispute in Congress that new legislation was needed, both to replace outdated authorization and also to underscore a bipartisan desire to defeat the terrorists seeking an Islamic state. The group has seized territory in Syria and Iraq, imposed a violent form of Sharia law and beheaded several hostages from the United States and other Western countries. Last week, it distributed a horrifying videotape showing the killing-by-burning of a Jordanian pilot.

Mueller's death was the latest event to produce calls for retaliation.

Among members of Obama's party, Rep. Steny Hoyer, D-Md., said during the day that some rank-and-file lawmakers want to set geographic limits and restrict the types of forces that can be used.

"They want some time limit so we can reconsider at some point in time, whether it's 24 months, 36 months, 48 months," he said at a news conference.

Republicans praised Obama's willingness to seek legislation, up to a point.

"This president, you know, is prone to unilateral action. But when it comes to national security matters, and particularly now fighting this barbaric threat -- not only to the region but to our own security -- I think it's important to come to Congress and get bipartisan support," said John Cornyn of Texas, the Senate's second-ranking Republican leader.

Many Republicans have said they prefer legislation that at least permits the use of ground troops if Obama decides they may be necessary. Some, including Sen. John McCain, have gone further, saying ground troops are needed if the Islamic State fighters are to be defeated.

Obama so far has relied on congressional authorizations that President George W. Bush used to justify military action after 9/11. He said last year he had the legal authority necessary 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.

Fox News' Chad Pergram and The Associated Press contributed to this report.