"A new era of American leadership is at hand," the president said.

But families of the 9/11 fallen slammed Obama for going soft on terrorists.

"The terrorists are going to be cheering," said FDNY Fire Lt. Jim McAffrey, whose brother-in-law, FDNY Battalion Chief Orio Palmer, was killed at Ground Zero.

"It's the wrong move. It sends a chilling message to people who are trying to fight the war on terror. These people are trying to kill us. Down the road, [Obama] may regret doing this."

Obama said he was certain the nation's security is strengthened when the United States adheres to "core standards of conduct."

"We think that it is precisely our ideals that give us the strength and the moral high ground to be able to effectively deal with the unthinking violence that we see emanating from terrorist organizations around the world," he said.

Retired FDNY Deputy Chief Jim Riches - whose firefighter son, Jimmy, died in the trade center's north tower - said he had just visited Guantanamo, and the detainees "get better medical treatment than the veterans."