Kerry will also testify Wednesday before the House Foreign Affairs Committee. Kerry and Director of National Intelligence James Clapper will hold a classified briefing Wednesday with members of the Senate Foreign Relations Committee.
Members of the House Democratic caucus participated in an unclassified conference call Monday with Obama national security adviser Susan Rice, Kerry, Hagel, Clapper and Dempsey.
Obama has said he wants limited military action to respond to an attack in the Damascus suburbs last month that the US says included sarin gas and killed at least 1,429 civilians, more than 400 of whom were children.
McCain and Graham, both Republicans, represent the most aggressive faction in Congress and have called on Obama to launch more comprehensive strikes with an aim of destroying President Bashar Assad's air power, his military command and control, Syria's ballistic missiles, and other military targets while at the same time increasing training and arming of opposition forces.
On the other side of the spectrum, some Republican and Democratic lawmakers don't want to see military action at all.
"I think it's very early for a lot of people and I think people are sceptical because they're hearing questions at home and they are surprised that the president decided to come to Congress," said Rep. Eliot Engel of New York, the top Democrat on the House Foreign Relations committee. Engel, appearing on CNN, says he supports Obama's position but said the president has to make his case to Congress.
The White House is engaging in what officials call a "flood the zone" persuasion strategy with Congress, arguing that failure to act against Assad would weaken any deterrence against the use of chemical weapons and could embolden not only Assad but also Iran and the Lebanese militant group Hezbollah.
Obama's turnabout decision to seek congressional authority on Syria sets the stage for the biggest foreign policy vote in Congress since the Iraq war.
On Sunday, Kerry said the US received new physical evidence in the form of blood and hair samples that shows sarin gas was used in the Aug. 21 attack. Kerry said the US must respond with its credibility on the line.
"We know that the regime ordered this attack," he said. "We know they prepared for it. We know where the rockets came from. We know where they landed. We know the damage that was done afterwards."
On Capitol Hill Sunday, senior administration officials briefed lawmakers in private to explain why the US was compelled to act against Assad. Obama, Vice President Joe Biden and White House Chief of Staff Denis McDonough also made calls to individual lawmakers.
"The American people deserve to hear more from the administration about why military action in Syria is necessary, what it will achieve and how it will be sufficiently limited to keep the US from being drawn further into the Syrian conflict," said Sen. Bob Corker of Tennessee, the top Republican on the Foreign Relations Committee, reflecting a more cautious approach to a military strike.
McCain said Obama asked him to come to the White House specifically to discuss Syria.
"It can't just be, in my view, pinprick cruise missiles," the Arizona Republican told CBS' "Face the Nation."
In an interview with an Israeli television network, he said Obama has "encouraged our enemies" by effectively punting his decision to Congress. He and Graham have threatened to vote against Obama's authorisation if the military plan doesn't seek to shift the momentum of the 2 1/2 year civil war toward the rebels trying to oust Assad from power.
Obama is trying to convince Americans and the world about the need for action.
So far, he is finding few international partners willing to engage in a conflict that has claimed more than 100,000 lives in the past 2 1/2 years and dragged in terrorist groups on both sides of the battlefield.
Only France is firmly on board among the major military powers. Britain's Parliament rejected the use of force in a vote last week.
Russia's foreign minister, Sergey Lavrov, said Monday the information the US showed Moscow to prove the Syrian regime was behind the chemical attack was "absolutely unconvincing".
With Navy ships on standby in the eastern Mediterranean ready to launch missiles, Congress on Sunday began a series of meetings that are expected to continue over the next several days in preparation for a vote once lawmakers return from summer break, which is scheduled to end September 9.
Senior administration officials gave a two-hour classified briefing to dozens of members of Congress in the Capitol on Sunday.
Lawmakers expressed a range of opinions coming out of the meeting, from outright opposition to strident support for Obama's request for the authorisation to use force.
Among Democrats, Rep. Sander Levin of Michigan said he'd approve Obama's request and predicted it would pass. Rep. Elijah Cummings of Maryland said he was concerned the authorization might be "too broad." Rep. Bennie G. Thompson, the senior Democrat on the House Homeland Security Committee, said the administration still has "work to do with respect to shoring up the facts of what happened".
Republican Rep. Cathy McMorris Rodgers of Washington said she was concerned about what Congress was being asked to approve. Sen. Jeff Sessions, R-Ala., said the war resolution needed tightening.
"I don't think Congress is going to accept it as it is," Sessions said.
Here's a look at key Syria developments around the world amid heightened tensions over potential military action:
SYRIA:
Assad said military strikes against his country would risk triggering a regional war. He said the Middle East is a "powder keg" and no one can say what will transpire if the West takes military action against Syria. He warned "the whole world will lose control of the situation. Chaos and extremism will spread. The risk of a regional war exists".
UNITED STATES:
Obama will host Sen. John McCain at the White House, hoping his opponent in the 2008 presidential election will help sell the idea of a US military intervention in Syria to a nation scarred by more than a decade of war. Sen. Lindsey Graham will also attend. The Obama administration is trying to rally support for the strike among Americans and their congressman and senators.
RUSSIA:
The Russian news agency Interfax said President Vladimir Putin hopes to send a delegation of lawmakers to the US to discuss the situation in Syria with members of Congress. Russian Foreign Minister Sergey Lavrov said evidence the US showed Moscow to blame the Syrian regime for the alleged chemical weapons attack was "absolutely unconvincing." He said "there was nothing specific" in the evidence.
TURKEY:
Turkish Prime Minister Recep Tayyip Erdogan's chief adviser brushed aside fears that a US strike against Syria could provoke Damascus to attack Turkey. Yalcin Akdogan told the Turkish daily newspaper Aksam that an attack on Turkey "would be madness and suicide" because Turkey is a member of NATO. The alliance is committed to defending member states.
FRANCE:
A French intelligence report estimated that the Syrian regime launched the alleged August 21 attack involving a "massive use of chemical agents" and could carry out similar strikes in the future. The government, on its website, published a 9-page intelligence synopsis about Syria's chemical weapons program that found that at least 281 deaths could be attributed to the attack in rebel-held areas outside Damascus.
CHINA:
Chinese Foreign Ministry spokesman Hong Lei said his country urged the US not to take unilateral action against Syria. He said Washington briefed Beijing about the matter and that China is concerned about chemical weapons use but that the country opposes the US acting alone. Hong didn't address the possibility of the US acting together with France's government, which supports a strike. Beijing would almost certainly be opposed to any strike.
GERMANY:
Chancellor Angela Merkel and her challenger in Germany's upcoming election said late Sunday they wouldn't participate in military action against Syria. Merkel said there must be "a collective answer by the UN" to the use of chemical weapons in Syria as she faced centre-left rival Peer Steinbrueck in a televised debate. Steinbrueck said he wouldn't participate in military action as chancellor and would "greatly regret it" if the US strikes alone without an international mandate.
- AP
