By Richard Cowan and Caren Bohan
WASHINGTON (Reuters) - The U.S. Congress, which votes largely along party lines on most issues, is displaying a different kind of split in the debate over Syria: Experienced lawmakers who support President Barack Obama's plans for military action are lining up against more skeptical and rebellious newcomers mostly from the ideological edges of both parties.
A similar pattern emerged earlier this year on a proposal to limit surveillance by the National Security Agency, which failed in the U.S. House of Representatives but attracted significant support both from Tea Party members and libertarians and Democratic liberals.
While the Republican leaders of the U.S. House of Representatives came out in support of Obama on Tuesday, a House Republican aide, who asked not to be identified, said he expected most Tea Party-backed Republicans, around 50 lawmakers, to vote against any resolution in the chamber, which currently has 433 voting members.
Their rationale, the aide said, is that the United States should not be involved in military action unless it is attacked.
The Democratic leadership of Congress is mostly supportive of Obama as well. But according to a rough count, about 30 or 35 Democrats in the House and four or five in the U.S. Senate have made statements leaning against military strikes.
While some are veteran liberals, most are newer arrivals such as Illinois freshman Representative Tammy Duckworth, an Iraq War veteran.
"Until I feel it's imperative to our national security, I will not support pre-emptive intervention in Syria," Duckworth said in a statement last week. "America shouldn't bear the burden unilaterally, especially since none of our allies, including those in the region, have committed to action."
Many say it is too early to call the vote. But some early estimates of how members could line up point to a group of House liberal Democrats, including some Congressional Black Caucus members, leaning against the resolution and joining hands with their ideological opposites - conservative and libertarian Republicans who eagerly have defied their leaders' wishes on several major issues earlier this year.
Obama has asked Congress to authorize limited action in response to what the administration says was a sarin gas attack by the Syrian government that killed more than 1,400 people, hundreds of them children, near Damascus on August 21.
The NSA vote earlier this year was on a proposal made jointly by conservative Representative Justin Amash and liberal Representative John Conyers, both from Michigan. The measure failed in the house by 12 votes, with 111 Democrats and 94 Republicans in support.
Particularly in the case of the Democrats, early statements do not mean they will ultimately cast a vote against military action in Syria.
The situation is evolving rapidly on Capitol Hill, and members do not yet know the actual wording of the resolution they will be asked to vote on, which is still being crafted.
Things looked relatively bleak for Obama on Monday, for example, but they improved significantly on Tuesday when the top leaders of the House - Republicans and Democrats - announced their support of a military operation.
Such endorsements do not carry as much weight as they did in years past, however. That was illustrated vividly shortly after House Speaker John Boehner announced his position, when young conservatives started bucking him.
"I'm new here," said Representative Trey Radel, a Tea Party Republican on the House Foreign Affairs Committee, which will craft a resolution authorizing military action against Syria. "But being new here, I am very skeptical of Republicans and Democrats that have dragged us into wars of the past."
The freshman Florida congressman added, "When we look at Afghanistan and Iraq, I am questioning still today what is the end goal within these countries; what have we accomplished with so many lives being lost."
"We are going to see a significant number of anti-war Democrats join with a new generation of neo-isolationist Republicans," said Norm Ornstein of the American Enterprise Institute.
"They will, in turn, be joined by some Republicans who might not believe those things but just don't want to vote for anything that Barack Obama is for," he said.
Ornstein said, however, that Obama is in "incomparably better shape today than he was two days ago" in his drive to win congressional approval of limited military action.
"These coalitions that are emerging are quite different than what we normally see, even on authorizations for war and defense/military related votes," said Sarah Binder, a Brookings Institution scholar.
"On the Republican side, the issues here are between a growing isolationist-conservative wing of both the House and Senate Republican conference, contrasted with more traditional conservative ‘war hawk' members of the Republican Party," she said.
"The question is, how deep do those divisions run?....I think it probably will be a close vote down to the wire."
Representative Steve Israel, a member of the House Democratic leadership, predicted a consensus will emerge that will overshadow the messy fight in the run-up to votes.
"At the end of the day, if a majority of the House of Representatives supports a form of this resolution, how we got there will be largely irrelevant," Israel predicted.
(Additional reporting by Thomas Ferraro; Editing by Fred Barbash and Lisa Shumaker)