WASHINGTON — The proposed 2017 federal spending bill would withhold billions in defense spending until the Trump administration submits its strategy to defeat the Islamic State group.

Of the $15 billion in supplemental wartime spending in a bipartisan deal reached Sunday, $2.5 billion would be withheld until 15 days after the president provides Congress with the strategy.

The congressional push for oversight would require the defense secretary and secretary of state update the Armed Services, Foreign Relations, Intelligence and Appropriations committees every 90 days. The bill also calls on the president to provide a strategy for Syria, though it does not tie any money to that.

How far the oversight push will go is unclear. Since U.S. President Donald Trump's election, Congress has had little debate and no vote on an authorization of the use of military force, as lawmakers may be reluctant to record their position or limit the president's war-fighting ability. The U.S. has been fighting ISIS under the post-9/11 authorization without Congress updating it.

Defense Secretary Jim Mattis told reporters in mid-April that the U.S. plans to focus on defeating ISIS without getting more deeply involved in Syria's civil war.

In late February, Mattis reportedly presented the White House with a classified plan to defeat ISIS, telling Congress last month the "skeleton plan" includes "economic, diplomatic, military, covert means."

"We should have this done in the next couple of months, if that long," Mattis said. "It may not even take us another month. But we're still putting it together."

Joint Chiefs Chairman Gen. Joseph Dunford, who appeared with Mattis, said the plan would "fully leverage all the capabilities our nation has: diplomatically, economically and militarily, and now in the 21st century in the information space as well."

The move comes as the White House has given the Pentagon greater flexibility to determine the number of U.S. troops in Iraq and Syria, another move by Trump to shift greater power to his military leaders.

That decision gives Mattis the authority to send more forces into Syria and to assist U.S.-backed local troops as they move to retake Raqqa from ISIS, which has used the city as a de facto capital. It will also let him adjust the force numbers in Iraq, in the ongoing fight to oust ISIS from Mosul and stabilize it as the rebuilding begins.

The Pentagon has already been making quiet, incremental additions to the troop levels in both countries in recent months, adding hundreds of Marines in Syria to provide artillery support and sending more advisers into Iraq to work with units closer to the fight in Mosul. Those moves were done with White House approval but without any formal adjustment to the longstanding troop caps that had been set by the Obama administration.

The Associated Press contributed to this report.

Email:  jgould@defensenews.com 

Twitter:  @reporterjoe 

Joe Gould is the Congress reporter for Defense News.