WASHINGTON — President Barack Obama began overhauling U.S. treatment of terror suspects Thursday, signing orders to close the Guantanamo Bay detention center, shut down secret overseas CIA prisons, review military war crimes trials and ban the harshest interrogation methods.

With his action, Obama started changing how the United States prosecutes and questions al-Qaida, Taliban or other foreign fighters who pose a threat to Americans — and overhauling America's image abroad, battered by accusations of the use of torture and the indefinite detention of suspects at the Guantanamo prison in Cuba.

"The message that we are sending the world is that the United States intends to prosecute the ongoing struggle against violence and terrorism and we are going to do so vigilantly and we are going to do so effectively and we are going to do so in a manner that is consistent with our values and our ideals," the president said.

The centerpiece order would close the much-maligned Guantanamo facility within a year, a complicated process with many unanswered questions that was nonetheless a key campaign promise of Obama's. The administration already has suspended trials for terrorist suspects at Guantanamo for 120 days pending a review of the military tribunals.

In the other actions, Obama:

—Created a task force to recommend policies on handling terror suspects who are detained in the future. Specifically, the group would look at where those detainees should be housed since Guantanamo is closing.

—Required all U.S. personnel to follow the U.S. Army Field Manual while interrogating detainees. The manual explicitly prohibits threats, coercion, physical abuse and waterboarding, a technique that creates the sensation of drowning and has been termed a form of torture by critics. However, a Capitol Hill aide says that the administration also is planning a study of more aggressive interrogation methods that could be added to the Army manual — which would create a significant loophole to Obama's action Thursday.

"We believe that the Army Field Manual reflects the best judgment of our military, that we can abide by a rule that says we don't torture, but that we can still effectively obtain the intelligence that we need," Obama said. He said his action reflects an understanding that "we are willing to observe core standards of conduct, not just when it's easy, but also when it's hard."

A task force will study whether other interrogation guidelines — beyond what's spelled out in the Army manual — are necessary for intelligence professionals in dealing with terror suspects.

But an Obama administration official said that provision should not be considered a loophole that will allow controversial "enhanced interrogation techniques" to be re-introduced. The official spoke on condition of anonymity to speak candidly about the administration's thinking.

The order also orders the CIA to close all its existing detention facilities abroad for terror suspects — and prohibits those prisons from being used in the future. The agency has used those secret "black site" prisons around the world to question terror suspects.

—Directed the Justice Department to review the case of Qatar native Ali al-Marri, who is the only enemy combatant currently being held on U.S. soil. The directive will ask the high court for a stay in al-Marri's appeals case while the review is ongoing. The government says al-Marri is an al-Qaida sleeper agent.

An estimated 245 men are being held at the U.S. naval base in Cuba, most of whom have been detained for years without being charged with a crime. Among the sticky issues the Obama administration has to resolve are where to put those detainees — whether back in their home countries or at other federal detention centers — and how to prosecute some of them for war crimes.

"We intend to win this fight. We're going to win it on our terms," Obama said as he signed three executive orders and a presidential directive.

The administration official said Obama's government will not transfer detainees to countries that will mistreat them, including their own home country.

In his first Oval Office signing ceremony, Obama was surrounded by retired senior military leaders. He described them as outstanding Americans who have defended the country — and its ideals.