(Fixes typo in penultimate paragraph)

* Obama administration has appointed two prosecutors

* Lieberman says this does not go far enough

* White House defends "very thorough investigation"

WASHINGTON, June 17 (Reuters) - A Senate committee chairman called on Sunday for a special counsel to investigate suspected leaks of U.S. classified information following allegations that the White House made the disclosures to boost President Barack Obama's election chances.

Senator Joseph Lieberman, chairman of the Senate Homeland Security and Governmental Affairs Committee, said U.S. Attorney General Eric Holder's appointment on June 8 of two federal prosecutors to investigate the suspected leaks did not go far enough.

"We need a special counsel because a special counsel avoids any appearance of conflict of interest," Lieberman said on "Fox News Sunday."

"Special counsels - independent counsels before them - were created for situations exactly like this where people might reach a conclusion that investigators, U.S. attorneys even, working for the attorney general - who was appointed by the president - cannot independently and without bias investigate high officials of their own government."

The secrets, revealed in media stories, have included reports on U.S. cyber warfare against Iran, procedures for targeting militants with drones and the existence of a double agent who penetrated a militant group in Yemen.

Republicans have already demanded an outside special counsel to investigate the leaks. Lieberman is an independent who caucuses with the Democrats in the Senate and usually votes with them.

Holder said the investigation would be headed by U.S. Attorneys Ronald Machen Jr. of Washington and Rod Rosenstein of Maryland, who would be "fully authorized to prosecute criminal violations discovered as a result of their investigation."

Senior White House adviser David Plouffe defended the Obama administration's approach in the leaks investigation.

"This ought to be investigated as thoroughly as anything can and we ought to wait for the results of that investigation," Plouffe said on the same program.

"There's going to be a very thorough investigation," he added.

Plouffe was asked if Obama would sit down with the investigators but declined to answer. Asked if Obama had declassified the information that ended up in published reports, Plouffe said, "No, of course he didn't."

The investigation by the two federal prosecutors is likely to include scrutiny of White House officials, sources have told Reuters.

The issue has spilled into the presidential campaign, with some Republicans charging the leaks appear calculated to boost the Democratic president's re-election prospects on Nov. 6. Obama has said he has "zero tolerance" for these kinds of leaks.

Lieberman said the leaks were "the worst in a long time" and called for stronger U.S. laws to prevent future leaks.

"In my opinion, an enormous amount of damage has been done to our national security," Lieberman said. "In the case of the cyber attack on Iran ... this is the first confirmation of that. Some methods of how it was carried it out were telegraphed to the Iranians. I think there's a danger that it may legitimize an Iranian or terrorist counter-cyber attack on us."

Lieberman said the leaks had also angered the operative who infiltrated Yemen-based al Qaeda in the Arabian Peninsula.

"This will discourage people and foreign intelligence services from cooperating with us in the future," Lieberman said. (Reporting by Will Dunham, Bill Trott, David Brunnstrom and Thomas Ferraro; Editing by David Brunnstrom)

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  • Dianne Feinstein, Saxby Chambliss, Mike Rogers, C.A. "Dutch" Ruppersberger

    After a closed-door meeting with National Intelligence Director James Clapper, the four leaders of the House and Senate Intelligence Committees hold a news conference, on Capitol Hill in Washington, Thursday, June 7, 2012, to discuss the recent spate of classified national security information leaks. From left are Rep. C.A. "Dutch" Ruppersberger, D-Md., the ranking Democrat on the House Intelligence Committee; House Intelligence Committee Chairman Mike Rogers, R-Mich., Sen. Saxby Chambliss, R-Ga., vice-chair of the Senate Intelligence Committee, and Senate Intelligence Committee Chair Sen. Dianne Feinstein, D-Calif. (AP Photo/J. Scott Applewhite)

  • Dianne Feinstein, Saxby Chambliss, Mike Rogers, C.A. "Dutch" Ruppersberger

    After a closed-door meeting with National Intelligence Director James Clapper, the four leaders of the House and Senate Intelligence Committees hold a news conference, on Capitol Hill in Washington, Thursday, June 7, 2012, to discuss the recent spate of classified national security information leaks. From left Rep. C.A. "Dutch" Ruppersberger, D-Md., the ranking Democrat on the House Intelligence Committee; House Intelligence Committee Chairman Rep. Mike Rogers, R-Mich., Senate Intelligence Committee Chair Sen. Dianne Feinstein, D-Calif.; and Sen. Saxby Chambliss, R-Ga., vice-chair of the Senate Intelligence Committee. (AP Photo/J. Scott Applewhite)

  • Dianne Feinstein, Saxby Chambliss, Mike Rogers, C.A. "Dutch" Ruppersberger

    After a closed-door meeting with National Intelligence Director James Clapper, the four leaders of the House and Senate Intelligence Committees hold a news conference, on Capitol Hill in Washington, Thursday, June 7, 2012, to discuss the recent spate of classified national security information leaks. From left are, Rep. C.A. "Dutch" Ruppersberger, D-Md., the ranking Democrat on the House Intelligence Committee; House Intelligence Committee Chairman Rep. Mike Rogers, R-Mich., Senate Intelligence Committee Chair Sen. Dianne Feinstein, D-Calif.; and Sen. Saxby Chambliss, R-Ga., vice-chair of the Senate Intelligence Committee. (AP Photo/J. Scott Applewhite)

  • James Clapper

    Director of National Intelligence James Clapper, center, emerges from a closed-door meeting with the House and Senate Intelligence Committees aimed at stopping security leaks, Thursday, June 7, 2012, on Capitol Hill in Washington. (AP Photo/J. Scott Applewhite)

  • James Clapper

    Director of National Intelligence James Clapper, center, emerges from a closed-door meeting with the House and Senate Intelligence Committees aimed at stopping security leaks, Thursday, June 7, 2012, on Capitol Hill in Washington. (AP Photo/J. Scott Applewhite)

  • Jay Carney

    Press Secretary Jay Carney briefs reporters at the White House in Washington, Monday, June 4, 2012. (AP Photo/Charles Dharapak)

  • House Leader Boehner And Cantor Respond To Obama's Economic News Conference

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  • House Leader Boehner And Cantor Respond To Obama's Economic News Conference

    WASHINGTON, DC - JUNE 08: House Majority Leader Eric Cantor (R-VA) (L) and U.S. Speaker of the House John Boehner (R-OH) (R) respond to U.S. President Barack Obama's remarks on the U.S. economy June 8, 2012 in Washington, DC. During their remarks, Cantor said, 'Did he see the job numbers that came out last week? The private sector is not doing fine. And, frankly, I'd ask the president to stop engaging in the blame game.' (Photo by Win McNamee/Getty Images)

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    WASHINGTON, DC - JUNE 08: U.S. Speaker of the House John Boehner (R-OH) arrives to respond to U.S. President Barack Obama's remarks on the U.S. economy June 8, 2012 in Washington, DC. During remarks with House Majority Leader Eric Cantor, Cantor said, 'Did he see the job numbers that came out last week? The private sector is not doing fine. And, frankly, I'd ask the president to stop engaging in the blame game.' (Photo by Win McNamee/Getty Images)

  • House Leader Boehner And Cantor Respond To Obama's Economic News Conference

    WASHINGTON, DC - JUNE 08: House Majority Leader Eric Cantor (R-VA) (L) and U.S. Speaker of the House John Boehner (R-OH) (R) respond to U.S. President Barack Obama's remarks on the U.S. economy June 8, 2012 in Washington, DC. During their remarks, Cantor said, 'Did he see the job numbers that came out last week? The private sector is not doing fine. And, frankly, I'd ask the president to stop engaging in the blame game.' (Photo by Win McNamee/Getty Images)

  • House Leader Boehner And Cantor Respond To Obama's Economic News Conference

    WASHINGTON, DC - JUNE 08: U.S. Speaker of the House John Boehner (R-OH) (R) and House Majoirty Leader Eric Cantor (R-VA) (L) respond to U.S. President Barack Obama's remarks on the U.S. economy June 8, 2012 in Washington, DC. During Cantor's remarks, Cantor said, 'Did he see the job numbers that came out last week? The private sector is not doing fine. And, frankly, I'd ask the president to stop engaging in the blame game.' (Photo by Win McNamee/Getty Images)