* U.S. official sees good case for extradition under treaty
* U.S. hacked Chinese mobile phone companies -report
* Snowden sought representation from rights lawyers -sources (Adds details, background)
By Steve Holland and Phil Stewart
WASHINGTON, June 22 (Reuters) - The United States said on Saturday it wants Hong Kong to extradite Edward Snowden and urged it to act quickly, paving the way for what could be a lengthy legal battle to prosecute the former National Security Agency contractor on espionage charges.
Legal sources say Snowden, who is believed to be hiding in Hong Kong, has sought legal representation from human rights lawyers since leaking details about secret U.S. surveillance activities to news media.
"If Hong Kong doesn't act soon, it will complicate our bilateral relations and raise questions about Hong Kong's commitment to the rule of law," a senior Obama administration official told Reuters, speaking on condition of anonymity.
U.S. National Security Adviser Tom Donilon told CBS News the United States had a "good case" to bring Snowden back to America to face trial and expected Hong Kong to comply with its extradition treaty.
"We have gone to the Hong Kong authorities seeking extradition of Snowden back to the United States," Donilon said.
He added that U.S. law enforcement officials were in a "conversation" with Hong Kong authorities about the issue.
A senior U.S. law enforcement source said extradition "can, of course, be a lengthy legal process" but expressed optimism that Snowden would be sent back to the United States.
The South China Morning Post reported that Snowden was not detained or in police protection - as reported elsewhere - and instead he was in a "safe place" somewhere in Hong Kong.
The paper also quoted Snowden offering new details about America's spy activities, including accusations of U.S. hacking of Chinese mobile phone companies and targeting China's top Tsinghua University.
"The NSA does all kinds of things like hack Chinese cellphone companies to steal all of your SMS (texting) data," Snowden was quoted by the newspaper as saying in a June 12 interview.
Documents previously leaked by Snowden revealed that the NSA has access to vast amounts of internet data such as emails, chat rooms and video from large companies, including Facebook and Google, under a government program known as Prism.
They also showed that the government had worked through the secret Foreign Intelligence Surveillance Court to gather so-called metadata - such as the time, duration and telephone numbers called - on all calls carried by service providers such as Verizon.
On Friday, the Guardian newspaper, citing documents shared by Snowden, said Britain's spy agency GCHQ had tapped fiber-optic cables that carry international phone and internet traffic and is sharing vast quantities of personal information with the NSA.
The United States charged Snowden with theft of government property, unauthorized communication of national defense information and willful communication of classified communications intelligence to an unauthorized person, according to the June 14 criminal complaint made public on Friday.
The latter two offenses fall under the U.S. Espionage Act and carry penalties of up to 10 years in prison.
Scores of Americans have been sent back home from Hong Kong to face trial under the extradition treaty. But the process can take years, lawyers say, and Snowden's case could be particularly complex.
America's use of the Espionage Act against Snowden has fueled debate among legal experts about whether that could complicate his extradition, since the treaty includes an exception for political offenses and Hong Kong courts may choose to shield him from prosecution.
Snowden says he leaked the details of the classified U.S. surveillance to expose abusive and illegal programs that trampled on citizens' privacy rights.
President Barack Obama and his intelligence chiefs have vigorously defended the programs, saying they are regulated by law and that Congress was notified. They say the programs have been used to thwart militant plots and do not target Americans' personal lives.
Stephen Vladeck, a professor at American University's Washington College of Law who studies national security issues, said there is no clear definition of what constitutes a political offense under the treaty.
"My intuition says it'll be easier for Snowden to argue espionage is a political offense than (the U.S. charge of) theft of government property," Vladeck said.
Should he return to the United States, Snowden would face trial in a federal court in Virginia that has a long track record of hearing cases related to national security and also to cyber crime.
In the past 20 years, the U.S. government has racked up remarkable success rates in winning convictions or guilty pleas from people brought before the federal court in Virginia who were accused of espionage or terrorism. Because of its speed, the court is considered a "rocket docket." (Additional reporting by James Pomfret, Venus Wu and Grace Li in Hong Kong, Diane Bartz in Washington and Nate Raymond in New York.; Writing by Phil Stewart.; Editing by Eric Beech and Christopher Wilson)