* In Washington, lawmakers call for aggressive prosecution
* Snowden faces possible extradition battle in Hong Kong
* Online, signs of support for contractor who leaked secrets (Adds details, quotes throughout)
By John Whitesides
WASHINGTON, June 10 (Reuters) - A contractor at the National Security Agency who leaked details of top-secret U.S. surveillance programs dropped out of sight in Hong Kong on Monday ahead of a likely push by the U.S. government to have him sent back to the United States to face charges.
Edward Snowden, 29, who provided the information for published reports last week that revealed the NSA's broad monitoring of phone call and Internet data from large companies such as Google and Facebook, checked out of his Hong Kong hotel hours after going public in a video released on Sunday by Britain's Guardian newspaper.
The disclosures by Snowden have sent shockwaves across Washington, where several lawmakers called on Monday for the extradition and prosecution of the ex-CIA employee who was behind one of the most significant security leaks in U.S. history.
There were some signs, however, that Snowden's stance against government surveillance and his defense of personal privacy was resonating with at least some Americans.
Supporters flocked to Snowden's aid on the Internet - more than 25,000 people signed an online petition urging Obama to pardon Snowden even before he has been charged. A separate effort on Facebook to raise funds for Snowden's legal defense netted nearly $8,000 in just a few hours.
In Hong Kong, officials were cautious in discussing a spy drama that could entangle U.S.-China relations just a few days after U.S. President Barack Obama and Chinese President Xi Jinping met at a summit in California where cyber security was a prime topic.
Snowden told the Guardian that he went to Hong Kong in hopes it would be a place where he might be able to resist U.S. prosecution attempts, although the former British colony has an extradition treaty with the United States.
On Monday, some local officials suggested that Snowden might have miscalculated.
"We do have bilateral agreements with the U.S. and we are duty-bound to comply with these agreements. Hong Kong is not a legal vacuum, as Mr. Snowden might have thought," said Regina Ip, a Hong Kong lawmaker and former security secretary.
Snowden said he turned over the documents to The Washington Post and the Guardian in order to expose the NSA's vast surveillance of phone and Internet data.
The former technical assistant at the CIA, who had been working at the NSA as an employee of contractor Booz Allen Hamilton, said he became disenchanted with Obama for continuing the surveillance policies of George W. Bush, Obama's predecessor.
"I don't want to live in a society that does these sort of things ... I do not want to live in a world where everything I do and say is recorded," Snowden told the Guardian, which published the video interview with him, dated June 6, on its website.
In Washington, several members of Congress and intelligence officials showed little sympathy for Snowden's argument. The U.S. Justice Department already is in the initial stages of a criminal investigation.
"Anyone responsible for leaking classified information should be punished to the fullest extent of the law," said Republican Mike Rogers, chairman of the House of Representatives Intelligence Committee.
'A SACRED TRUST'
James Clapper, the director of national intelligence, told NBC that the leaks "violate a sacred trust for this country. The damage that these revelations incur are huge."
Some lawmakers were more cautious, however, saying the surveillance programs revealed by the Guardian and The Post raised concerns not just about citizens' privacy, but also whether the Obama administration had done enough to keep Congress informed about such surveillance, as required by law.
"The government does not need to know more about what we are doing. We need to know more about what the government is doing," said Ron Paul, a former House member and unsuccessful Republican presidential candidate in 2012 who has long said that the U.S. government is too intrusive into Americans' daily lives.
"We should be thankful for individuals like Edward Snowden," Paul said.
At the White House on Monday, Obama spokesman Jay Carney sidestepped questions about Snowden. Responding to questions about the White House's efforts to brief Congress about the NSA's surveillance programs, a senior administration official released a list of 22 briefings that had been conducted for lawmakers over a 14-month span.
There will be more briefings on Tuesday, when a half-dozen national security, law enforcement and intelligence officials will meet with House members. The Senate will be briefed on Thursday.
Snowden, who the Guardian said had been working at the NSA for four years as a contractor for outside companies, told the Guardian he had copied the secret documents at the NSA office in Hawaii three weeks ago and had told his supervisor that he needed "a couple of weeks" off for epilepsy treatments. He flew to Hong Kong on May 20.
Staff at a luxury hotel in Hong Kong told Reuters that Snowden had checked out at noon on Monday. Ewen MacAskill, a Guardian journalist, said later in the day that Snowden was still in Hong Kong.
"He didn't have a plan. He thought out in great detail leaking the documents and then deciding rather than being anonymous, he'd go public. So he thought that out in great detail. But his plans after that have always been vague," MacAskill said.
"I'd imagine there's now going to be a real battle between Washington and Beijing and civil rights groups as to his future," MacAskill said. "He'd like to seek asylum in a friendly country but I'm not sure if that's possible or not."
HONG KONG ASYLUM POLICY 'IN LIMBO'
Legally speaking, where does Snowden go from here?
If Snowden is charged on criminal counts as many lawmakers and officials expect, the focus will turn to the extradition treaty that the United States and Hong Kong signed in 1996, a year before the former British colony was returned to China.
The treaty, which allows for the exchange of criminal suspects in a formal process that also may involve the Chinese government, went into effect in 1998.
It says that Hong Kong authorities can hold a U.S. suspect for up to 60 days after the United States submits a request indicating there is probable cause to believe the suspect violated U.S. law. In Snowden's case, such a request could lead Hong Kong authorities to hold him while Washington prepares a formal extradition request.
Snowden could try to stay in Hong Kong by seeking political asylum. Simon Young, a professor of law at the University of Hong Kong, said there are strong protections for people making asylum claims under Hong Kong's extradition laws.
A decision this year by Hong Kong's High Court requires the government to create a new standard for reviewing asylum applications, putting the cases on hold until the new system is finished.
"He's come really at probably the best moment in time because our asylum laws are in a state of limbo," Young said.
MORE REVELATIONS TO COME?
Snowden's revelations launched a broad national debate on privacy rights and the limits of security programs in the aftermath of the Sept. 11, 2001, attacks in the United States.
On Monday, Glenn Greenwald, the Guardian's lead reporter on the Snowden case, used Twitter to chide Clapper for claiming that Snowden's disclosures harmed national security. Greenwald also suggested that there were more revelations to come.
"Clapper: leaks "literally gut-wrenching" - "huge, grave damage" - save some melodrama and rhetoric for coming stories. You'll need it," Greenwald tweeted.
Many members of Congress have expressed support for the surveillance program but raised questions about whether it should be more tightly supervised and scaled back.
"In my mind, things that may have been appropriate in the aftermath of 9/11 and in the weeks and months and even years after that, may no longer be appropriate today," Republican Representative Luke Messer of Indiana said on MSNBC.
Some officials said the U.S. government might need to reconsider how much it relies on outside defense contractors who are given top security clearances. As of October 2012, about 483,000 government contractors has top-secret security clearances, according to a report issued in January by the Office of the Director of National Intelligence.
"We do need to take another, closer look at how we control information and how good we are at identifying what people are doing with that information," said Stewart Baker, former general counsel at the NSA and former assistant secretary for policy at the Department of Homeland Security. (Additional reporting by James Pomfret, David Ingram, Mark Hosenball, Susan Heavey, Patricia Zengerle; Editing by David Lindsey, Jim Loney and Mohammad Zargham)