SAN JUAN, Puerto Rico -- The number of Guantanamo Bay detainees participating in a hunger strike has ballooned from three to around 75, the U.S. military said Monday, revealing growing defiance among prisoners held for up to 4 1/2 years with no end in sight.

Navy Cmdr. Robert Durand called the hunger strike at the U.S. naval base in southeastern Cuba an "attention-getting" tactic to step up pressure for the inmates' release and said it might be related to a May 18 clash between detainees and guards that injured six prisoners.

"The hunger strike technique is consistent with al-Qaida practice and reflects detainee attempts to elicit media attention to bring international pressure on the United States to release them back to the battlefield," Durand said from Guantanamo Bay.

The United States now holds about 460 people at Guantanamo on suspicion of links to al-Qaida or the Taliban. But human rights groups say innocent people have been sent to the jail.

Defense lawyers said the hunger strike, which began last year, reflects increasing frustration among men who have little contact with the world outside the remote prison.

"I think it is escalating because the people down there are getting more and more desperate," said Bill Goodman, legal director for the New York-based Center for Constitutional Rights, which represents many of the detainees. "Obviously, things have reached a crisis point."

The military did not release the names of the striking detainees, and lawyers said they have no way of learning whether their clients are involved until they can visit the base.

"All these men want is a chance to have a trial," said Zachary Katznelson, an attorney for Reprieve, a British human rights group that represents 36 Guantanamo detainees. "If they are guilty, punish them. If not, then send them home."

Only 10 of the prisoners have been charged and face trial before military tribunals. The U.S. Supreme Court is expected to rule in June whether President Bush overstepped his authority in ordering the tribunals.

Durand said the number of hunger strikers reached about 75 over the weekend. U.S. officials classify detainees as being on hunger strike when they have missed nine consecutive meals.

Some 76 detainees began the strike last August to protest their confinement, with their ranks peaking at 131 in the fall, the military has said.

Defense lawyers have accused the military of underreporting the number of hunger strikers.

The lawyers say the number of strikers dwindled to three earlier this year after the military adopted more aggressive measures to force feed them, including using a restraint chair. U.S. officials said the measures are "safe and humane" and have been used in American civilian prisons.

Four of the detainees on hunger strike are being force-fed, including the three who were participating in the protest before the recent increase, Durand said.

Military officials believe the increase in hunger strikers was timed to coincide with the arrival of journalists and lawyers for the next round of pretrial hearings for Guantanamo detainees in June, Durand said.

He added it also could be related to the clash earlier this month in which, according to the military, a detainee pretended to commit suicide to lure guards into a cellblock, where they were attacked by prisoners armed with makeshift weapons.

Earlier that day, two detainees overdosed on antidepressant drugs they collected from other detainees and hoarded in their cells. The men have since regained consciousness.