In a 273 to 156 vote, the House voted Wednesday in favor of arming and training moderate Syrian rebels as part of President Obama's plan to fight the Islamic State. (Reuters)

The House on Wednesday approved President Obama’s plan to train and equip moderate Syrian rebels to counter the growing threat of the Islamic State organization, even though lawmakers in both parties remain deeply skeptical about its chances for success.

The vote placed Congress one step closer to authorizing the third significant U.S. military operation in Iraq in the past quarter century, and it put lawmakers on record approving U.S. engagement in the years-long Syrian civil war. It delivered Obama much-needed domestic political support as he seeks an international coalition to combat the growing threat of Islamist terrorism in the Middle East.

But the tally — 273 to 156 — also revealed widespread misgivings in both parties about the plan’s chances of success, even among lawmakers who voted in favor of it.

Obama’s proposal was opposed by more than 40 percent of Democrats, many of whom are concerned that new U.S. military operations in the Middle East could fester for several years with no clear strategy or definition of success.

Republicans provided the lion’s share of support, but many are worried that Obama’s plans are too limited. One top GOP leader suggested that Congress could give the president blanket military authority, even if Obama doesn’t want it, when lawmakers hold a much broader debate after the November elections about the fight against Islamist militants.

On Tuesday afternoon, President Obama told troops at MacDill Air Force Base in Tampa, Fla., that "100 percent of Americans need to support" them and their families. He told them he would not commit them to "a ground war" in Iraq. (WhiteHouse.gov)

Obama on Wednesday repeated his promise not to send ground forces into the military campaign against the Islamic State, telling troops in a speech at Florida’s MacDill Air Force Base that he will “not commit you . . . to fighting another ground war in Iraq.”

In a statement after the House vote, Obama said, “There will be no U.S. military personnel in Syria as part of this program. We’ve learned over the last decade, and through our successful campaign to degrade al-Qaeda, that it is more effective to use America’s unique capabilities to take out terrorist targets in support of our partners’ efforts on the ground to secure their own future.”

The amendment authorizing Obama’s plans was part of a short-term spending bill keeping the federal government operating through mid-December. Supporters included 159 Republicans and 114 Democrats, while 85 Democrats and 71 Republicans voted against the amendment. The Senate is expected to give the bill final approval Thursday.

In more than six hours of debate spread over two days, few House lawmakers stepped forward to give a full-throated endorsement of the Obama plan. Every ideological corner of the House found reason to doubt the mission, portending a lengthy debate in November and December over an expansive use-of-force resolution. Some Democrats are eyeing tighter constraints on military engagement, and some Republicans are trying to expand the battlefield.

Several lawmakers who are military veterans or are still serving in the armed forces voted against the authorization. Rep. Duncan D. Hunter (R-Calif.), a Marine who deployed to Iraq and Afghanistan, said the authority “does nothing” to destroy the Islamic State. Rep. Tulsi Gabbard (D-Hawaii), a captain in the Hawaii National Guard who served in Iraq, called Obama’s strategy “unrealistic” and worried “it will take way too long” to work.

But some of the earliest opponents of entering Iraq in 2003 found themselves voting yes while offering little assurance of military success. “It’s the best choice of worse options,” said Rep. James P. Moran (D-Va.), a retiring lawmaker who voted against authorizing the Iraq war 12 years ago. “It’s because there are no better alternatives and I don’t think it’s responsible to do nothing.”

Some of Obama’s closest congressional allies also expressed deep skepticism. “I have hesitations and concerns about the blank check we gave George Bush,” said Rep. Steve Israel (N.Y.), chairman of the Democratic Congressional Campaign Committee, who has worked closely with Obama to raise money for House candidates.

Israel supported the authorization Wednesday but said many Democrats would push for language in the fall to prevent the mission from resembling Iraq in 2005 and 2006, when the deadliest fighting took place.

“The one thing I know is that ISIL is a fundamental threat and it needs to be addressed,” he said, using a common acronym for the Islamic State.

House Majority Whip Steve Scalise (R-La.) said most Republicans are ready to “revisit the broader question” of U.S. military action in the Middle East. In an interview this week, Scalise said the idea of drafting a new authorization for military action “has come up a lot,” including “if more should be done, should it be authorized by Congress even if the president isn’t asking for it?”

Rep. Kristi L. Noem (R-S.D.) said she would welcome a comprehensive debate. She voted for authorization Wednesday, but said in an interview beforehand that “I’m not convinced this is the silver bullet, I think this is going to be a longer, more drawn-out process.”

GOP leaders were helped Wednesday morning when the Club for Growth, an influential conservative group, decided not to include the vote on the government funding bill on its scorecard for GOP lawmakers. The group informed House lawmakers in a memo that while it remains opposed to the underlying spending plans, it doesn’t take positions on legislation “driven by foreign policy.”

The retreat by many conservative groups came a year after they cheered on a budget impasse that led to a partial government shutdown, reflecting the muddled nature of Wednesday’s debate.

After the Club for Growth’s announcement, House GOP leaders sought to bolster support by making calls to several lawmakers. So did House Minority Leader Nancy Pelosi (D-Calif.) and her lieutenants, although their efforts were “soft touches,” or informal outreach, according to aides.

Senior White House staffers and Obama were credited for engaging House Republicans, especially Speaker John A. Boehner (Ohio) and Majority Leader Kevin McCarthy (Calif.), with direct calls between the principals seen as an expression of good faith, according to aides in both parties.

In the Senate, Majority Leader Harry M. Reid (D-Nev.) was preparing to hold a vote on the spending measure Thursday. But he will not earn unified support from Democrats.

Sen. Joe Manchin III (D-W. Va.) said Wednesday that he opposes granting Obama expanded authorities because he is not convinced new military operations will succeed.

“We have been at war in that part of that world for the past 13 years,” he said. “If money and military might could have made a difference, it would have by now.”

Sen. Bob Corker (Tenn.), the ranking Republican on the Senate Foreign Relations Committee, co-authored the first bill to help train and arm rebels in Syria, but said Wednesday that he is unsure how the new legislation would work. The pro-Western rebels Corker originally envisioned training are still mostly focused on fighting the regime of Syrian President Bashar al-Assad rather than Islamic State forces.

“There’s a major disconnect,” Corker said, smacking his head for emphasis.

Still, Corker said he plans to support the limited operation in anticipation of a longer debate later this year. “They don’t have a plan, they don’t have a strategy,” Corker said of the White House, adding, “They’re doing it to eke by the midterm elections.”

In anticipation of a bigger debate, Sen. Timothy M. Kaine (D-Va.), who plans to vote for the authorization, unveiled proposed language for a new use-of-force measure. His plan, which would expire after a year, would repeal the current congressional authorization for military force in Iraq and prohibit the deployment of U.S. combat forces in Iraq and Syria. Kaine said his proposal would also define the types of “associated forces” that the U.S. could partner with in the region, including Iraqi and Kurdish military forces.

“If they won’t participate and carry the ground campaign, there’s no amount of U.S. or Western troops that will enable this mission to be successful,” he said.

Robert Costa, Sebastian Payne and Wesley Lowery contributed to this report.