WASHINGTON — The hard core of detainees held at America’s Guantanamo Bay detention camp will be held indefinitely even if there is insufficient evidence to bring them to trial, a senior Bush administration official said.

Of the 435 detainees being held at Guantanamo, only 10 have so far been charged with terrorism-related offenses. A further 14 detainees — the so-called high value detainees such as the alleged mastermind of the September 11 attacks, Khalid Sheikh Mohammed — are also expected to face trial now that the U.S. Congress has passed the Military Commission Act, which will finally enable America to commence trials of Guantanamo detainees next year.

But of the remainder, an estimated 200 detainees face being held indefinitely at Guantanamo because they are deemed a threat to international security even though there is insufficient evidence to bring them before a military commission.

John Bellinger, the legal adviser at the U.S. State Department who is responsible for defending Guantanamo’s legal status, said the hard core of the detainees will continue to be held indefinitely either because they are considered a security threat or because there is nowhere to send them if the military authorities at Guantanamo decide to release them.

“The remaining people — other than the ones who have been approved for release — really do pose a threat,” Mr. Bellinger said in an exclusive interview with the Daily Telegraph. “Ten percent of the people we have released have gone right back to fighting generally in Afghanistan. It’s hard to tell exactly how many people would go back to actual acts of terrorism, or whether they would just go back to fighting in Afghanistan.”

And despite repeated calls for the Bush administration to close Guantanamo, Mr. Bellinger was insistent that the American detention camp in Cuba would continue to hold detainees that were deemed a security risk.

“There are at this point no plans to transfer those people from Guantanamo out of Guantanamo,” he said. “At this point the trials will be held on Guantanamo.”

More than 700 people have been held at Guantanamo during the past five years. Most of them were detained during the war in Afghanistan to overthrow the Taliban in late 2001, while others have been transferred to the camp after being detained as part of America’s global war against international terrorism.

All the detainees receive a yearly combatant status review tribunal at which American military officials determine whether or not individuals continue to pose a security threat. Nearly 300 detainees have so far been released, and Mr. Bellinger said a further 100 had been cleared for release.

But Mr. Bellinger said Washington had been frustrated in its attempts to reduce the number of people being held at Guantanamo by the refusal of countries to accept released detainees.

“Many countries will just not take their nationals back,” said Mr. Bellinger. “We think it is somewhat hypocritical of international critics to keep calling for the closure of Guantanamo without offering a place for any of these individuals.”

But, Mr. Bellinger insisted, those detainees who are still classified a security risk will continue to be held at Guantanamo indefinitely. “When people say Guantanamo should be closed, do they really want” the detainees “to be released outright into their countries where they might go out and continue to pose a threat to the international community?”

In the case of alleged high-value detainees such as Khalid Sheikh Mohammed, they might never be released, even if it was not possible to bring a successful prosecution against them. “Khalid Sheikh Mohammed is unlikely to be sent anywhere” other than Guantanamo, he said.