"We're exploring all alternatives as to how best to do the main objective, which is to protect America. What we don't want to do is let somebody out that comes back and harms us," Bush said in an interview with Fox News Channel on Wednesday.
Calls for closure of the prison camp for foreign terrorism suspects at Guatanamo Bay, Cuba, have risen over the past few days after Amnesty International set off a furore last month by calling it a "gulag" and comparing it to the brutal Soviet system of forced labour camps in which millions died.
Nancy Pelosi, the Democratic leader of the House of Representatives, added her voice to the criticism on Wednesday by supporting those calling for the closure of the detention camp, including former president Jimmy Carter and Senator Joseph Biden, the senior Democrat on the Senate Foreign Relations Committee.
"I think that we need a fresh start, ... a clean slate for America in the Muslim world," Pelosi said.
The prison camp has been dogged by allegations of abuse since it was created in the aftermath of the 11 September 2001 attacks and the subsequent US-led military action in Afghanistan.
However, the Pentagon this week ruled out closing Guantanamo.
It was disclosed last week that American guards or interrogators at Guantanamo had mishandled the Quran, Islam's holy book, by stepping on it and soaking it in water.
In one case, a guard's urine splashed through an air vent on to a prisoner and his Quran.
"We're exploring all alternatives as to how best to do the main objective, which is to protect America. What we don't want to do
is let somebody out
that comes back and harms us"
President George Bush
Bush said the prisoners at Guantanamo were treated fairly and rejected as absurd the description of it as a gulag.
"I will tell you that we treat these prisoners in accordance with international standards. And that's what the American people expect," he said.
But Pelosi's support added weight to the argument that the prison is harming US image abroad.
Pelosi's comments came less than a day after Carter, a Democrat renowned across the globe for championing human rights causes, urged the US to shut down the prison.
He said that detainees should be treated fairly and given due process under the law.
"To demonstrate clearly our nation's historic commitment to protect human rights, our government needs to close down Guantanamo and the two dozen secret detention facilities run by the United States as soon as practicable," Carter said.
"To demonstrate clearly our nation's historic commitment to protect human rights, our government needs to close down Guantanamo and the two dozen secret detention facilities run by the United States as soon as practicable"
Former president Jimmy Carter
Biden, a Democrat from Delaware, declared the detention camp "the greatest propaganda tool that exists for the recruiting of terrorists around the world".
The Guantanamo prison, which is located at a US naval base in Cuba, was opened in January 2002.
While many former detainees have already been released or sent back to their home countries, it still holds about 520 non-US citizens, most of them captured in Afghanistan and detained without charges for more than three years.