Even as House Speaker John Boehner said he would support a military attack against Syria for its apparent use of chemical weapons, President Barack Obama appears to have the legal authority to order strikes without congressional approval.

Emerging from a White House meeting Tuesday with Obama and congressional leaders from both parties, Boehner, R-West Chester Twp., predicted the House would support the president in approving cruise missile and possible air attacks against the regime of Syrian President Bashar al-Assad.

“We have enemies around the world that need to understand that we’re not going to tolerate this kind of behavior,’’ Boehner said in forceful language. “We also have allies around the world and allies in the region who also need to know that America will be there and stand up when it’s necessary.’’

Boehner’s announcement — combined with Sen. John McCain’s decision Sunday to back an attack on Syria — increases the chances that Congress will approve a resolution when both chambers take up the measure next week.

Michael Steel, a Boehner spokesman, acknowledged it remains “an uphill battle to pass a resolution.’’ But even if one house rejects the resolution, Obama has made it clear that under the Constitution he has “the authority to carry out this military action.’’

Presidents since the dawn of the Republic have sent U.S. troops abroad scores of times without a vote by Congress, ranging from President William McKinley to China in 1900 to deal with the Boxer Rebellion to President Harry Truman to South Korea in 1950 to repel a North Korean invasion.

By contrast, Congress has only declared war 11 times, including against Spain in 1898, Germany in 1917, and Japan and Germany in 1941. On a handful of other occasions — such as the 1991 and 2003 attacks on Iraq — Congress authorized military action without a formal declaration of war.

“As a matter of domestic law, it’s pretty clear he’s got that authority and that has been exercised by a large number of presidents in the past,’’ said William Howard Taft IV, former legal adviser to the State Department and grandson of the former president and cousin of former Gov. Bob Taft.

But a president’s power in this instance is “very muddled,” according to John Quigley, a professor of international law at Ohio State University.

Quigley said the president is commander-in-chief, but he contended that “means you command them’’ after war is authorized by Congress. With Syria, Quigley said “this is a bit of stretch’’ to argue the president can on his own launch an attack “which doesn’t involve any threat to the United States.’’

Boehner’s support is crucial for the White House to win House backing for the use of force. Although as many as 80 House Republicans are likely to oppose a resolution, Boehner probably could sway the votes of more than 120 other Republican lawmakers.

Among those expected to oppose the resolution is Rep. Mike Turner, R-Dayton, who said Tuesday he “would be incredibly surprised if the House of Representatives passed this resolution.’’ Turner said during a conference call Sunday with members of the House Armed Services Committee, it was “pretty uniform that people were opposed to this action.”

Before the closed-door meeting with congressional leaders, Obama told reporters “the military plan that has been developed by the joint chiefs — and that I believe is appropriate — is proportional. It is limited. It does not involve boots on the ground. This is not Iraq and this is not Afghanistan.’’

Obama said the attacks “will send a clear message not only to the Assad regime, but also to other countries that may be interested in testing some of these international norms, that there are consequences.’’

“It gives us the ability to degrade Assad’s capabilities when it comes to chemical weapons,’’ Obama said. “It also fits into a broader strategy that we have to make sure that we can bring about over time the kind of strengthening of the opposition and the diplomatic and economic and political pressure required so that ultimately we have a transition that can bring peace and stability not only to Syria but to the region.’’