The White House pushed forward aggressively on Monday for Congressional approval of an attack on Syria as President Obama got tentative support from one of his most hawkish Republican critics, Senator John McCain of Arizona, for a “limited” strike — as long, Mr. McCain said, as the president did more to arm the Syrian opposition.
After an hourlong meeting with Mr. Obama at the White House, Mr. McCain emerged with Senator Lindsey Graham, Republican of South Carolina, to say that the two senators’ discussions with Mr. Obama in the Oval Office had been “encouraging.” He also urged Congress to support Mr. Obama in his plan for military action in Syria, saying that a no vote would be “catastrophic” for the United States and its credibility in the world.
The words from Mr. McCain were a positive development for the White House and a critical part of the Obama administration’s lobbying blitz on Syria on Monday. The day got off to a start with a 70-minute telephone briefing to the House Democratic Caucus by Secretary of State John Kerry; Defense Secretary Chuck Hagel; Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff; Susan E. Rice, the national security adviser; and James R. Clapper Jr., the director of national intelligence.
There were 127 House Democrats on the call, nearly two-thirds of their total number. Democrats on the call said the debate was shifting away from whether the Assad government had used chemical weapons in a massacre last week — several Democrats said the material cited as evidence by the administration was persuasive — and more toward how should the administration should respond.
“The debate is shifting away from, did he use chemical weapons, to what should be done about it?” Representative Adam B. Schiff, a California Democrat on the House Intelligence Committee, said in a telephone interview.
There was also a strong sense on the call, Democrats said, that Mr. Obama needs to appeal directly to American public, most likely in a prime-time address.
On the call, Mr. Kerry took the lead, portraying the horrors of chemical weapons and underscoring the consequences of inaction. General Dempsey reviewed possible targeting, and how the military is planning strikes that minimize threat to civilians. He also reprised the argument that delay does not help President Bashar al-Assad despite his dispersal of troops and equipment. Mr. Clapper reviewed unclassified intelligence, particularly his view of why rebels could not have launched poison gas attack. Ms. Rice played maestro and traffic cop and assigned questions from lawmakers to the briefers.
Although Mr. McCain and Mr. Graham have been sharply critical of Mr. Obama that a strike he is planning on Syria would not be extensive enough, many more lawmakers in both parties have taken the opposite approach of Mr. McCain and Mr. Graham, saying they were wary of a strike on Syria, no matter how limited.
On Tuesday, Mr. Obama is to meet with the leadership of the Senate Armed Services Committee, the Senate Foreign Relations Committee, the Senate Select Committee on Intelligence, and their counterparts in the House.
Administration officials said the influential pro-Israel lobby group Aipac was already at work pressing for military action against the government of Mr. Assad, fearing that if Syria escapes American retribution for its use of chemical weapons, Iran might be emboldened in the future to attack Israel. In the House, the majority leader, Eric Cantor of Virginia, the only Jewish Republican in Congress, has long worked to challenge Democrats’ traditional base among Jews.
One administration official, who, like others, declined to be identified discussing White House strategy, called Aipac “the 800-pound gorilla in the room,” and said its allies in Congress had to be saying, “If the White House is not capable of enforcing this red line” against the catastrophic use of chemical weapons, “we’re in trouble.”
In France, the only nation to offer vigorous support for an American attack, there were rising calls for a parliamentary vote like the one in last week in Britain, where lawmakers jolted the White House with a rejection of a British military attack. But the French government, in an effort to bolster its case, released a declassified summary of French intelligence that it said ties Mr. Assad’s government to the use of chemical weapons on Aug. 21.
In Russia, Foreign Minister Sergey V. Lavrov dismissed as unconvincing the evidence presented by Mr. Kerry of chemical weapons use by the Syrian government. “We were shown certain pieces of evidence that did not contain anything concrete, neither geographical locations, nor names, nor evidence that samples had been taken by professionals,” Mr. Lavrov said in a speech at the Moscow State Institute of International Relations.
In Israel, President Shimon Peres offered strong support for Mr. Obama’s decision to seek the backing of Congress , saying he had faith in the president’s “moral and operational” position. “I recommend patience,” Mr. Peres said in an interview on Army Radio. “I am confident that the United States will respond appropriately to Syria.”
In Washington, the White House’s “flood the zone” effort, as one official called it, will continue. Classified briefings will be held for all House members and senators on Tuesday, Thursday and Friday.
On Tuesday, Mr. Obama has invited the Republican and Democratic leaders of the House and Senate defense, foreign affairs and intelligence committees to the White House. But that night, he departs on a long-planned foreign trip, first to Sweden and then to Russia for the annual G-20 summit meeting of major industrialized and developing nations, a forum that is sure to be dominated by talk of Syria, and bring Mr. Obama face-to-face with Mr. Assad’s chief ally and arms supplier, President Vladimir V. Putin of Russia.
House Democrats on the conference call with administration officials, which lasted 70 minutes, said Mr. Kerry, who has been the most aggressive and public prosecutor for military action, took the lead. Democrats said he portrayed not only the horrors of chemical weapons inflicted on Syrian civilians in the Aug. 21 attacks outside Damascus, but also the potential threat, if left unanswered, that such weapons posed to regional allies like Israel, Jordan and Turkey.
Mr. Kerry argued that inaction could embolden Iran or nonstate terrorists to strike those Middle East allies, and further encourage Iran and North Korea to press ahead with their nuclear programs.
“One of the important propositions that Kerry put to members was, are you willing to live with the consequences of doing nothing?” said Representative Gerald E. Connolly, a Virginia Democrat.
The secretary of state addressed lawmakers’ concern that the United States should have international support. “The United States will not go it alone,” he said at one point, according to a senior Democrat who declined to be identified. Offers of “military assets” have come from France, Saudi Arabia, Turkey and the United Arab Emirates, he said, without identifying the assets, and more are expected.
In the week since the Obama administration began moving toward a military strike on the Assad government, Mr. Kerry said, the Syrian military has seen about 100 defections, including 80 officers.
General Dempsey reviewed the range of possible targets and how the Pentagon is planning strikes that would minimize risk to civilians. Despite reports that Syrian commanders were moving troops and equipment into civilian neighborhoods, General Dempsey told lawmakers, as he had assured Mr. Obama, that delaying military action would not weaken the effectiveness of any military attack. He suggested that military officials would adjust their targets to address changes on the ground.
The general acknowledged that the United States could not prevent the Assad government from using chemical weapons again, but said the military had “additional options” should a first missile strike not deter a retaliatory strike by Mr. Assad, including in defense of critical allies, presumably Israel, Jordan and Turkey. That scenario, however, describes just the escalating conflict some opponents fear.
“My constituents are skeptical that a limited effort will not mushroom into a full-blown boots on the ground,” said Representative Elijah E. Cummings, a Maryland Democrat.
Mr. McCain, who has been arguing for two years that the United States should support a moderate Syrian opposition, said he had strongly urged the president on Monday to provide anti-tank and antiaircraft systems to the opposition and to attack the Syrian air force.
Mr. Obama indicated that “he favorably viewed the degrading of Bashar al-Assad’s capabilities as well as upgrading the Free Syrian Army,” Mr. McCain said in an interview.
Administration officials have told Congress that the C.I.A.’s program to arm the rebels would be deliberately limited at first to allow a trial run for American officials to monitor it before ramping up to a larger, more aggressive campaign. American officials have been wary that arms provided to the rebels could end up in the hands of Islamic extremists with ties to Al Qaeda.