Deputy National Security Advisor Ben Rhodes tells reporters that the Islamic State is a greater threat now than it has been in the past. (Reuters)

Deputy National Security Advisor Ben Rhodes tells reporters that the Islamic State is a greater threat now than it has been in the past. (Reuters)

The Obama administration is considering seeking congressional authorization for military action against the Islamic State under a revamped counter­terrorism strategy President Obama announced last year.

A mandate from Congress could provide domestic legal justification for the unlimited use of force against the Sunni Muslim group across Iraq and Syria, a senior administration official said. Congress last formally authorized such action in 2001, against al-Qaeda and its associates, and 2002, against Iraq under Saddam Hussein.

The new authorization is one of several alternatives under active internal discussion as the administration grapples with whether and how to try to militarily defeat the Islamic State, which controls a wide swath of territory between Damascus and Baghdad.

The “range of options” for direct use of the U.S. military includes temporary authority under the War Powers Resolution, constitutional authority for emergency action to protect U.S. citizens, and “having that discussion with Congress” about a more open-ended authorization to combat the Islamic State, the official said.

Obama has ordered airstrikes in Iraq under the first option, good for 60 days until early October. The second option was used this summer to launch a failed rescue attempt of American hostages held by the Islamic State in Syria. The third would entail a debate with an uncertain outcome among lawmakers with widely divergent views on presidential powers and overseas military action.

The official did not rule out the immediate use of airstrikes or other action in Syria if necessary to protect U.S. citizens. The recent military raid, which was unsuccessful in locating four hostages, was followed by this week’s videotaped beheading of one of the captives, journalist James Foley.

“If you come after Americans, we are going to come after you,” deputy national security adviser Benjamin Rhodes told reporters Friday. “We’re not going to be restricted by borders.”

Foley’s execution “represents a terrorist attack against our country,” Rhodes said. The administration believes that it provides international legal justification for military action under self-defense doctrines.

While contingency plans for broader airstrikes in Syria have been prepared for presidential review should Obama ask for them, so far he has not. Nor has the intelligence community drawn up a list of high-value targets among individual Islamic State leaders, as it did with al-Qaeda, the senior official said.

“We’re obviously trying to find them,” the official said. But “we haven’t made a decision” on whether to target individuals. The official spoke on the condition of anonymity to discuss closed-door policymaking and intelligence matters.

While it formulates a more comprehensive, long-term policy, the official said, the administration is focused on driving the extremists out of Iraq and containing them in Syria. The Iraq policy is “a convergence of U.S. airstrikes, more arms and training” for Iraqi and Kurdish forces, and persuading Sunni communities to reject the militants, the official said.

“There are going to be gaps to fill” in that strategy, “and that’s what we are looking at now,” the official said.

Islamic State forces­ advanced into Iraq from Syria in the spring, quickly capturing the northern city of Mosul and rapidly moving south to within 60 miles of Baghdad. While the administration sent additional assistance to the Iraqi military, it used the promise of still more aid as leverage to force a change in Iraq’s government.

But while the government formation process was still underway, the extremists switched their focus toward Iraq’s Kurdish region, threatening to overrun one of the most peaceful areas of the country, where hundreds of American diplomats and civilians were present.

On Aug. 7, Obama authorized airstrikes against Islamic State fighters who were moving toward Irbil, the Kurdish capital in northern Iraq, and who had encircled and threatened to kill tens of thousands of members of the minority Yazidi sect.

The success of those ongoing strikes — now numbering nearly 100 over the past two weeks — and progress in forming a new, more inclusive version of Iraq’s Shiite-led government, have encouraged policymakers. The belief is that neighboring Sunni-led states, including Saudi Arabia, Jordan and Turkey, will help persuade Iraq’s Sunnis to turn away from the extremists and join their government’s fight against them.

For its part, the administration expects to continue airstrikes in Iraq for the foreseeable future, although it is “mindful” that it will soon have to address the 60-day war powers restriction, the senior official said. “We always know that as we evaluate how long we may need to take military action, there are limits on what can be done under war powers.”

“Separately,” the official said, “we have to make a similar judgment about any action in Syria.”

The situation in Syria is far more complicated. In Iraq, where the administration believes local forces­ can push the Islamic State back with some American assistance, airstrike objectives are limited to protection of U.S. personnel and facilities and humanitarian missions. U.S. action was requested by the Iraqi government.

In Syria, where a full-scale civil war is raging, the United States supports a weak rebel force that is fighting the government of President Bashar al-Assad as well as the Islamic State and other extremist groups.

Obama, who has ruled out U.S. ground forces­ in Syria or Iraq, has resisted any direct U.S. military action in Syria and has limited the aid he is prepared to provide rebel forces­ out of concern that it would fall into the hands of extremists. Although the CIA is training and equipping a number of rebel fighters, a larger program that would allow the U.S. military to assist is held up in congressional consideration of the defense budget.

An expanded covert program that would allow Islamic State forces­ to be targeted by drones, such as the CIA effort against al-Qaeda and the Taliban in Pakistan, is deemed risky. Not only do the extremists have surface-to-air missiles, but Assad’s forces control the air over Syria.

Authority for any military action, should it be seen as feasible and desirable, could theoretically be found under the existing 2001 Authorization for the Use of Military Force, or AUMF, against al-Qaeda.

“Three years ago, they would have clearly fit,” the senior administration official said of the Islamic State. But al-Qaeda’s Pakistan-based core announced last year that it had split with the group, objecting to its brutality against Muslims and declaration of an Islamic caliphate across Syria and Iraq. Now, officials are not certain whether that is a case worth making.

The administration has said it favors repeal of the Iraq AUMF, and some lawmakers have said the same about the al-Qaeda measure. Obama, in a May 2013 speech outlining a new, long-term counter­terrorism strategy, called it “outdated” with the dwindling power of al-Qaeda.

At the time, administration officials said the goal was to eliminate the broadly worded measure — which has been used to justify U.S. military action against groups labeled al-Qaeda “associates” in Yemen and Somalia — as a way of narrowing presidential power.

Authority to deal with new, more specific threats could be sought from Congress on a case-by-case basis, the officials said.

“If you look back on the president’s speech, he kind of foreshadows going to have additional” AUMFs, the official said. “It may be that this is the first case.”