By Lidia Kelly
MOSCOW (Reuters) - Edward Snowden's disappearance from view has heightened speculation that the former U.S. spy agency contractor may be talking to Russian secret services, which see him as a "tasty morsel" that is too good to miss.
Even a flat denial by President Vladimir Putin on Tuesday is unlikely to end whispers that Snowden may have been interviewed by intelligence officers anxious to get their hands on whatever information he has not yet leaked.
Some experts say Russia might even try to hand him over to the United States in a Cold War-style exchange, although this seemed less likely after Putin ruled out his extradition to face espionage charges back home.
"He is a tasty morsel for any, any secret service, including ours. Any secret service would love to talk to him," said a Russian security source.
Snowden, charged with disclosing secret U.S. surveillance programs, left Hong Kong for Moscow on Sunday and the WikiLeaks anti-secrecy group said he was heading for Ecuador, where he wants political asylum.
Russia's Federal Security Service (FSB) did not immediately respond to a request for comment by Reuters. But a former officer of its Soviet predecessor, the KGB, said Russia was unlikely to miss out, assuming Snowden is willing to cooperate.
"It would be silly to pass on such an opportunity to get information that is very difficult, impossible or expensive to get in any other way," said the ex-officer, Lev Korolkov.
U.S. Senator John McCain, a Republican opponent of President Barack Obama, said Putin - also a former Soviet agent - would grab the chance. "He is ... an old KGB colonel apparatchik that has disdain for democracy and the things we stand for and believe in," McCain said on CNN on Tuesday. "If he sees a situation he'll take advantage of it."
Speculation about an FSB role in Snowden's arrival from Hong Kong began with the plane's touchdown on Sunday, when about two dozen plain-clothed security agents were spotted monitoring the transit zone, at times accompanied by uniformed policemen.
Ecuador's ambassador to Russia, Patricio Alberto Chavez Zavala, got to the transit zone soon after Snowden landed. Then the agents and police blocked the entrance to one of the lounges. Some remained all night and into the next day,
But there was no sign of Snowden, who Putin said on Tuesday was still in the transit area at Sheremetyevo airport.
Snowden has said he accepted a job as a systems administrator at contractor Booz Allen Hamilton, where he worked for about three months, to gain access to details of the U.S. National Security Agency's surveillance programs.
U.S. officials said intelligence agencies were concerned they did not know how much sensitive material Snowden had, and that he may have taken more documents than initially estimated which could get into the hands of foreign intelligence agencies.
ASSESSING SNOWDEN'S VALUE
Russian political analyst Pavel Salin suggested the Kremlin's near silence on Snowden for more than 36 hours after he arrived was a stalling tactic. "Now they are assessing how useful he may be. His value depends on the information he has," he said.
Korolkov said that is unclear. "We don't know what really is in his possession and how much of an interest he is. All that he can say could already be known," he said. "But he is of interest (to Russia) for a number of other reasons."
Analysts said Snowden could be useful for a Cold War-style spy swap or as a propaganda tool for Russia, which frequently accuses the United States of violating the principles of freedom and democracy that it tries to press on others.
Putin, asked on Tuesday about the U.S. request to hand Snowden over, questioned whether the American and WikiLeaks founder Julian Assange, who is also a fugitive from justice, should be treated as criminals and jailed.
Deputy parliament speaker Vladimir Zhirinovsky has proposed Snowden be exchanged for Viktor Bout, a Russian arms dealer whose jailing in the United States angered Moscow. The United States has refused Russian requests for his repatriation.
Korolkov, and the security service source who spoke on condition of anonymity, said Russia would follow a common international practice in using Snowden in negotiations over Bout. "This is how it is done in the world. It would be in the government's advantage not to give Snowden back," Korolkov said.
The source said: "Russia has some negotiating advantage here."
But there are risks for both countries in taking the dispute over Snowden too far.
"It's a very, very important moment for the entire U.S.-Russia relationship: We are really at a point that will define the relationship for the foreseeable future," said Dmitry Trenin, director of the Carnegie Moscow Center think-tank.
Korolkov predicted the Kremlin will tread carefully. "Russia is not at all interested in entering into a conflict with such a geopolitical opponent and political partner as the United States," he said.
(Additional reporting by Gabriela Baczynska, Thomas Grove and Alissa de Carbonnel; Editing by Timothy Heritage, Steve Gutterman and David Stamp)