President Barack Obama, center, hosted a bipartisan meeting at the White House with House and Senate leaders to discuss the growing threat of the Islamic State in Iraq and Syria on Sept. 9. (Jim Lo Scalzo/EPA)

President Obama’s plan to train and equip Syrian rebels in the fight against Islamic State militants appeared headed for quick passage on Capitol Hill this week, but congressional leaders have signaled that they will postpone a full debate on the use of military force until after the midterm elections.

House Speaker John A. Boehner (R-Ohio) and Senate Minority Leader Mitch McConnell (R-Ky.) have been working together on a cross-chamber strategy designed to keep their party ranks united and move swiftly toward passage of the measure.

The House is expected to grant Obama the short-term authority as part of an amendment to a larger measure funding federal agencies that is expected to pass after it is debated Tuesday and Wednesday, GOP leadership aides said. Once the House votes, the Senate would take up the issue by next week before adjourning for the elections.

“People are trying to be careful about making a large commitment before we have all the facts, but eventually we need to have a new authorization that’s simple and sweeping and empowers the president to use all means necessary to destroy ISIL,” said Rep. Tom Cole (R-Okla.), using an alternative acronym for the Islamic State. “Hopefully that can happen in the lame-duck session.”

Rep. Adam Kinzinger (R-Ill.) said Monday that GOP colleagues who once favored not intervening in foreign conflicts seem to be in retreat. “It’s hard for them to argue to do nothing, and they know it,” he said.

On the international stage, Obama’s effort to build a broad coalition against the militants seemed to pick up momentum in Paris. World powers meeting in the French capital agreed to use “any means necessary” to combat the militant force surging in Iraq and Syria, and diplomats from 26 nations and several international organizations began dividing responsibilities for what Secretary of State John F. Kerry said will be an expanded international military, diplomatic and law enforcement assault on the group.

There was one setback in the coalition-building efforts. Iran on Monday spurned an American request for cooperation in the fight against the Islamic State. U.S. officials, however, said the door remains open to a rare opportunity for Iran to make common cause with the United States against its principal adversary in the Middle East.

Meanwhile on Monday, U.S. military officials said they conducted two airstrikes in Iraq, including one near Baghdad that they characterized as the start of a new phase of offensive operations against the Islamic State. Prior to the attack near Baghdad, which targeted Islamic State fighters who had been firing on Iraqi security forces, the U.S. military said its rules of engagement were to launch strikes only to prevent humanitarian disasters or protect U.S. personnel and property.

In Washington, Congress returned to work Monday with the Syria question at the top of the agenda, and leading members of both parties signaled a willingness to grant Obama’s request for explicit authority to allow U.S. military personnel to train rebels and outfit them with arms, at least in the short term.

Some disgruntled members of the president’s party, however, were insisting on a full war debate before the elections.

“I can’t see a reason to not do so, other than political timidity,” Rep. Adam B. Schiff (D-Calif.), a senior member of the House Intelligence Committee, said Monday.

“It’s very difficult to pinpoint how this issue cuts politically right now,” he added. “My sense is that it will have greater resonance in the next election than this one, depending on the nature of the conflict two years from now.”

Boehner’s decision to quickly introduce legislation underscores his hawkish view and the progress he has made to mollify his unruly conference and keep it moving in the same direction. The relative calm in GOP ranks contrasts with the unrest seen in the party a year ago, when daily battles over legislative strategy led to a government shutdown and badly divided the party. This year, Sen. Rand Paul (R-Ky.), who has long espoused non-interventionist views, has said he would like to “destroy” the Islamic State, and Sen. Ted Cruz (R-Tex.), who led the shutdown fight for conservatives, has avoided issuing any ultimatum.

“I would like to think Rand Paul and Ted Cruz are going through adolescence and beginning to enter adulthood,” said Rep. Peter T. King (R-N.Y.). “I think we’re back, as Republicans, to realizing that there is real danger in the world and that shutting down the government isn’t appropriate when you’re dealing with issues of life and death.”

Under plans unveiled by House Republicans on Monday night, Congress would grant short-term authorization for the Pentagon to begin operations to counter the rise of the Islamic State terrorist group. The Pentagon would be required to submit planning reports to lawmakers with details on how military officials are recruiting and vetting rebel forces.

Opening the Paris conference, French President François Hollande said the threat from global militancy requires a coordinated international response. France is among the European nations alarmed by the flow of radicalized young men who have traveled from Europe to fight in Syria and who could seek to return home.

The meeting came at the end of Kerry’s week-long tour of Iraq, Saudi Arabia, Egypt and Turkey. The trip sought to frame the division of labor for a wider assault on the Islamic State, with the U.S. military and Iraqi forces playing the central roles.

On Sunday, U.S. officials said Arab states have volunteered to launch airstrikes alongside those carried out by the United States. But they stressed that such an expansion was still under discussion and subject to review by Iraq. Officials from the region said the volunteers included Saudi Arabia, the United Arab Emirates and others whose leaders had been waiting to hear from the administration that it has a viable plan and is prepared to follow through with it.

The United Arab Emirates and Qatar conducted strikes during the 2011 air campaign in Libya. Qatar’s role is not entirely clear now, though it is helping train Syrian rebels, as is Jordan.

Saudi Arabia is also expected to participate in expanded training of the rebels fighting both the Islamic State and forces loyal to Syrian President Bashar al-Assad.

The Saudis have been pressing the United States to accede to Syrian rebels’ long-standing requests for surface-to-air antiaircraft weapons, which could be a game-changer for the chronically underequipped opposition forces, but the Obama administration has refused.

The U.S. decision to confront the militants, first in Iraq and eventually in Syria, also benefits Assad, although U.S. officials say they will act only in the interests of the United States.

As the international efforts gathered steam Monday, Iran played spoiler. Its supreme leader, Ayatollah Ali Khamenei, tweeted his disdain for the international effort and revealed a back-channel U.S. offer of unspecified cooperation against the militants. Khamenei said Iran rejected the U.S. request because of Washington’s “evil intentions,” the state-run Islamic Republic News Agency reported.

The United States did not deny the outreach to Iran and said discussions with Tehran will continue, underscoring Iran’s influence in the region as well as the political complexities of bringing the Shiite powerhouse into the emerging international alliance against the Islamic State. “I’m just going to hold open the possibility always of having a discussion that had the possibility of being constructive,” Kerry said, without providing substantive details about the U.S. request. “I’m not going to get into a back-and-forth.”

By going public with the U.S. offer Monday, Iran appeared to close off the possibility of cooperation against the militants for now.

However, Iran has sent its allied Shiite militias in Iraq to fight with Western-backed Kurds against the Islamic State. Iran’s Shiite theocracy considers the Sunni militants a challenge to Iraq’s majority Shiites — whose political parties have close ties to Tehran — and a destabilizing force against Assad, Iran’s other main regional ally.

Although details of the U.S.-Iranian discussion remain vague, it appears to have been an offer of behind-the-scenes cooperation rather than public partnership. Any public cooperation with Iran would doom the emerging alliance between Iraq and Sunni Arab states in the Persian Gulf region and elsewhere that had feuded with Nouri al-Maliki, the former Iraqi prime minister. The Sunni states regard Iran with deep suspicion and considered Maliki, a Shiite partisan with strong ties to Tehran, as a pawn of Iran.

France had wanted to invite Iran to the talks, but the United States resisted the move. The United States is trying to stitch together a diverse alliance against the Islamic State and overcome reluctance among many states to intervene in any way in the Syrian conflict, now in its fourth year. Nearly 200,000 people have died in the Syrian fighting, according to the United Nations.

Kerry said Monday that Saudi King Abdullah had told him that if Iran attended Monday’s session, the Saudis would boycott. The United Arab Emirates had drawn the same line, Kerry said.

Gearan reported from Paris. Robert Costa, Paul Kane and Craig Whitlock in Washington contributed to this report.