NEWPORT, Wales — President Obama escalated the American response to the marauding Islamic State in Iraq and Syria on Friday, recruiting at least nine allies to help crush the organization and offering the outlines of a coordinated military strategy that echoes the war on terror developed by his predecessor, George W. Bush, more than a decade ago.

In his most expansive comments to date about how the United States and its friends could defeat ISIS, a once-obscure group of Sunni militants that has now upended the Middle East and overshadowed Al Qaeda, Mr. Obama said the effort would rely on American airstrikes against its leaders and positions, strengthen the moderate Syrian rebel groups to reclaim ground lost to ISIS, and enlist friendly governments in the region to join the fight.

While the president’s aides maintained that he has not yet decided to authorize airstrikes in Syria — which he has already done on a limited basis in Iraq — Mr. Obama likened his developing strategy on ISIS to the American effort against Al Qaeda in Pakistan’s tribal regions, which has relied heavily on airstrikes.

Mr. Obama has been under enormous pressure to articulate a way to counter ISIS, which has proclaimed itself an Islamic caliphate that knows no borders and has demonstrated ruthless behavior, including the videotaped beheadings of two Americans. After creating a political tempest by saying last week that his administration lacked a strategy, Mr. Obama sought on Friday to portray himself as spearheading the effort.