Still, the situation is very fluid. Nearly half of the 433-member House and a third of the 100-member Senate remain undecided.
By their statements or those of aides, only 30 members of the Republican-led House support intervention or are leaning in favor of authorizing the president to use force against Syrian President Bashar Assad's government in response to a chemical weapons attack last month. Some 192 House members outright oppose U.S. involvement or are leaning against authorization, according to the AP survey.
The situation in the Democrat-controlled Senate is better for Obama but hardly conclusive ahead of a potential vote next week. The AP survey showed those who support or are leaning in favor of military action holding a slight 34-32 advantage over those opposed or leaning against it.
Complicating the effort in the Senate is the possibility that a three-fifths majority may be required. Republican Sen. Rand Paul of Kentucky says he is going to filibuster.
Still, Sen. Harry Reid, the Democratic leader, predicted, "I think we're going to get 60 votes,"
Speaking to reporters Friday after a summit of world leaders in St. Petersburg, Russia, Obama acknowledged the difficulties he faces in seeking support for action. He said he would address the nation on Tuesday.
"It's conceivable at the end of the day I don't persuade a majority of the American people that it's the right thing to do," Obama said. But the president, who again would not say what he would do if Congress rebuffed him, expressed confidence that the people and their lawmakers would listen to his case.
"Failing to respond," he said, "would send a signal to rogue nations, authoritarian regimes and terrorist organizations that they can develop and use weapons of mass destruction and not pay a consequence."
Whatever Obama might decide, a rejection from Congress would have wide-ranging ramifications in the United States and abroad.
If the administration goes ahead with cruise missile strikes and other limited action against Syrian targets, it could risk a constitutional crisis with angry lawmakers ahead of other confrontations over raising the U.S. debt ceiling, funding the government, overhauling immigration law and implementing Obama's signature health care changes.
The alternative -- that is, stepping back after weeks of war-like threats -- could project weakness to an American foe that the U.S. says has repeatedly launched chemical weapons attacks. It also could send a signal to both allies and American enemies that the U.S. is too divided internally to back up its declarations with actions over everything from preventing Iran from developing nuclear weapons to containing the threat posed by North Korea's erratic, nuclear-armed dictatorship.
How difficult is Obama's challenge in Congress? Only 21 House members publicly back a resolution to attack Syria, and nine say they are considering giving their support. Some 100 House members oppose Obama's plan, and 92 say they are leaning against it.
Opposition runs deep among Republicans and Democrats. So far, GOP lawmakers stand 148-9 against military action, when accounting for leaners. Democrats are opposed by a tally of 44-21.
For Obama to succeed, he'll have to win about 90 percent of the undecided House members
-- or change the minds of those who are leaning against him.
Rep. Michael Grimm, R-N.Y., has already changed his mind, but not in Obama's favor.
"My initial reaction, as a Marine combat veteran, was to stand by the commander in chief and support immediate, targeted strikes," Grimm said. But since then, he said, he has heard from many constituents "who strongly oppose unilateral action at a time when we have so many needs here at home." He now believes the benefits of a U.S. strike won't outweigh "the extreme cost of war."
After a decade of war in Afghanistan and Iraq, polls have shown Americans consistently oppose intervention in Syria, a fact Obama acknowledged after meeting fellow leaders of the leading rich and developing nations Friday. He compared the current situation to previous crises when America had to engage for the good of the world.
"These kinds of interventions, these kinds of actions are always unpopular because they seem distant and removed," Obama said. "I'm not drawing an analogy to World War II, other than to say, you know, when London was getting bombed, it was profoundly unpopular, both in Congress and around the country, to help the British."
"The intervention in Kosovo, very unpopular, but ultimately I think it was the right thing to do and the international community should be glad that it came together to do it," he added. "When people say that it is a terrible stain on all of us that hundreds of thousands of people were slaughtered in Rwanda, well, imagine if Rwanda was going on right now and we asked should we intervene in Rwanda. I think it's fair to say that it probably wouldn't poll real well."
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Obama has support among House leaders of both parties.
Speaker John Boehner, R-Ohio, Majority Leader Eric Cantor, R-Va., and House Democratic leaders Nancy Pelosi of California and Steny Hoyer of Maryland are on board. But many rank-and-file members of both parties either oppose attacking Syria or are sitting on the sidelines until they learn more about the administration's plans and see which way the political momentum turns.
There is still plenty of time for the administration to convince House members who are undecided or who've publicly expressed skepticism about military engagement. Reluctant lawmakers are often swayed during closed-door meetings with colleagues and party leaders. Just a third of the House and Senate have participated in any of the classified briefings with administration officials over the past week, underscoring that their votes may still be winnable.
All House members are invited to a classified briefing on Monday night, after Congress officially returns from summer break. House Democrats will meet Tuesday morning with White House Chief of Staff Denis McDonough, and House Republicans will meet separately at the same time. In the Senate, Republicans and Democrats will hold their weekly policy luncheons on Tuesday, a day before a likely vote to move forward on a resolution authorizing force.
With Republicans, the administration has a more difficult challenge.
Boehner and Cantor have provided little indication they're willing to lobby for Obama's cause, even if they support it. It's also unclear how much they can deliver given that tea party and other conservative Republicans have repeatedly gone against Boehner.
Obama is not alone in his effort to drum up support.
Pro-Israel groups, including the American-Israel Public Affairs Committee, the Anti-Defamation League and the Simon Wiesenthal Center, all have released public statements and made private calls urging lawmakers to vote for military action in Syria.
Israeli Prime Minister Benjamin Netanyahu has said that the way the world reacts to chemical weapons use in Syria has implications for how it will handle Iran's nuclear program, putting one of Congress' favorite foreign leaders firmly in the "yes" camp.
Still, many of the most ardent supporters of the Jewish state in Congress aren't yet convinced. AIPAC is bringing some 250 activists to Washington next week to push for approval.
Few Republicans or Democrats contest the argument from U.S. intelligence that Assad carried out a sarin gas attack in the Damascus suburbs on Aug. 21.
Lawmakers' main doubts are: Will the limited strikes proposed deter a further chemical weapons attack? Will they inadvertently help al-Qaida-linked rebel units? And how will the Obama administration respond if Syria or Iran retaliates, without getting further involved?
"I think every member of Congress' perception is colored by what happened in Iraq," said Rep. Bruce Braley, D-Iowa, who is seeking a Senate seat in 2014 and is leaning against authorizing force. "If Iran responds to our sending cruise missiles into Syria by launching an attack into Israel, and then Israel retaliates, and Hezbollah retaliates against Israel, I have a hard time seeing how the United States avoids getting drawn into a broader regional conflict."
At several town hall meetings with lawmakers across the country this week, people have raised their voices against military involvement.
In Phoenix on Thursday night, Sen. John McCain, one of the strongest advocates of U.S. action, faced intense criticism from constituents.
Press; By BRADLEY KLAPPER and STEPHEN OHLEMACHER]
AP White House
Correspondent Julie Pace in Russia and reporters Donna Cassata,
Henry Jackson, Ken Thomas, Laurie Kellman, Kevin Freking, Matthew
Lee, Matthew Daly, Sam Hananel and Monika Mathur in Washington
contributed to this report.
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