By Matt Spetalnick

WASHINGTON (Reuters) - The head of the International Committee of the Red Cross on Thursday expressed opposition to the force-feeding of prisoners staging a mass hunger strike at the Guantanamo prison camp and said he urged President Barack Obama to do more to resolve the "untenable" legal plight of inmates held there.

ICRC president Peter Maurer made his case in talks with Obama and other top U.S. officials in Washington this week while a team from the Geneva-based group monitored the hunger strike by dozens of detainees at the U.S. Naval Base in Cuba. Many have been held for more than a decade without charge or trial.

The U.S. military says 43 of the 166 prisoners have refused food, while defense lawyers estimate that 100 to 130 inmates have joined in. Eleven have lost so much weight that they have been strapped down and force-fed liquid nutrients through tubes inserted into their noses.

The protest has cast a spotlight on the internationally condemned facility, which was opened by Obama's Republican predecessor, George W. Bush, to hold foreign terrorism suspects after the September 11, 2001, attacks on the United States.

Obama, confronted by steep legal and political obstacles, failed to keep his promise to close the prison within a year of taking office in 2009. The White House insisted on Thursday he remained committed to shutting it but offered no new path to doing so in his second term.

Signaling growing international concern, Maurer said the hunger strike, which began about two months ago, was a "symptom" of the prisoners' legal plight. Military officers, human rights monitors and lawyers for the inmates have said it reflects frustration at the failure to resolve their fate.

"The issue of Guantanamo is politically blocked in this country," Maurer told a Washington news conference. He said his message to Obama and his advisers was that "they should put all their energy" into reaching a compromise on Guantanamo.

CAUTIOUS CRITICISM

Treading carefully on whether prisoners should be force-fed, Maurer said ICRC's doctors backed the view of international medical groups, which have denounced the practice. An ICRC spokesman in Geneva said last month the humanitarian organization was against force-feeding and instead upholds the principle of allowing detainees to choose their fate.

"There is a discrepancy between the position of the United States and the ICRC. That's very much part of, a point on the agenda," Maurer said when pressed on the matter.

The ICRC depends heavily on Washington for funding and cooperation, and usually maintains confidentiality in its dealings with governments, especially on detainee issues.

Maurer said he had pressed Obama, senior administration officials and U.S. lawmakers to work harder to address the Guantanamo prisoners' legal predicament.

He said the main issues include delays in promised regular reviews of prisoners' cases and hold-ups in transfer to their home countries of those deemed no longer a security risk.

Obama has approved use of military tribunals to try some of the most dangerous suspects. But only nine prisoners have been charged or convicted of crimes, according to military records.

Congress has made it difficult to repatriate others. The United States will not send some back to their homelands because of instability or concerns over mistreatment, and most countries are reluctant to accept them for resettlement when the United States itself will not take any.

Last week, U.N. human rights chief Navi Pillay called on Washington to close the Guantanamo prison, saying the indefinite imprisonment of many detainees violated international law.

White House spokesman Jay Carney declined to comment on the hunger strike, the latest of several that have flared up at the prison camp since it opened in January 2002. But he told reporters in Washington: "We continue to be committed to closing that facility, in our national security interest."

Obama's original promise to close Guantanamo was part of an effort to turn the page on the Bush era, when the invasion of Iraq and the harsh treatment of mostly Muslim terrorism suspects damaged America's image in the Islamic world.

(Additional reporting by Jane Sutton in Miami; Editing By Alistair Bell)