05-13) 14:48 PDT WASHINGTON, (AP) --

President Barack Obama declared Monday he would try to block the court-ordered release of photos showing U.S. troops abusing prisoners, abruptly reversing his position out of concern the pictures would "further inflame anti-American opinion" and endanger U.S. forces in Iraq and Afghanistan. The White House had said last month it would not oppose an appeals court ruling that set a May 28 deadline for releasing dozens of photos from military investigations of alleged misconduct.

But American commanders in the war zones have expressed deep concern about fresh damage the photos might do, especially as the U.S. tries to wind down the Iraq war and step up operations against the Taliban and al-Qaida in Afghanistan.

When photos emerged in 2004 from the infamous U.S.-run Abu Ghraib prison in Iraq, showing grinning American soldiers posing with detainees — some of the prisoners naked, some being held on leashes — the pictures caused a huge anti-American backlash around the globe, particularly in the Muslim world.

Obama, explaining his change of heart on releasing the other photos, said they had already served their purpose in investigations of "a small number of individuals." Those cases were all concluded by 2004, and the president said "the individuals who were involved have been identified, and appropriate actions have been taken."

The Pentagon conducted 200 investigations into alleged abuse connected with the photos in question. The administration did not provide an immediate accounting of how they turned out.

"This is not a situation in which the Pentagon has concealed or sought to justify inappropriate action," Obama said of the photos. "In fact, the most direct consequence of releasing them, I believe, would be to further inflame anti-American opinion and to put our troops in greater danger."

Spokesman Robert Gibbs said release of photos from the cases would merely "provide, in some ways, a sensationalistic portion of that investigation."

Obama said later, "I want to emphasize that these photos that were requested in this case are not particularly sensational, especially when compared to the painful images that we remember from Abu Ghraib."

Still, he said he had made it newly clear: "Any abuse of detainees is unacceptable. It is against our values. It endangers our security. It will not be tolerated."

The effort to keep the photos from becoming public represented a sharp reversal from Obama's repeated pledges for open government, and in particular from his promise to be forthcoming with information that courts have ruled should be publicly available.

As such, it invited criticism from the more liberal segments of the Democratic Party, which want a full accounting — and even redress — for what they see as the misdeeds of the Bush administration.

"The decision to not release the photographs makes a mockery of President Obama's promise of transparency and accountability," said ACLU attorney Amrit Singh, who had argued and won the case before the 2nd U.S. Circuit Court of Appeals in New York. "It is essential that these photographs be released so that the public can examine for itself the full scale and scope of prisoner abuse that was conducted in its name."

On Capitol Hill, Republicans welcomed the change, however. A military group also said it was relieved.

"These photos represent isolated incidents where the offending servicemen and women have already been prosecuted," said Brian Wise, executive director of Military Families United. "There is no good that can come from releasing these photos."

The reactions were a reverse of what happened after Obama's decision last month to release documents that detailed brutal interrogation techniques used by the CIA against terror suspects. Those also came out in response to an ACLU lawsuit, and his decision then brought harsh and still-continuing criticism from Republicans.

This time he's kicking the decision back into court, where his administration still may be forced into releasing the photos.

Indeed, there is some evidence that the administration has little case left.

Gibbs said the president instructed administration lawyers to challenge the photos' release based on the national security implications. He said that argument was not used before.

But the Bush administration already argued against the release on national security grounds — and lost.

"It is plainly insufficient to claim that releasing documents could reasonably be expected to endanger some unspecified member of a group so vast as to encompass all United States troops, coalition forces, and civilians in Iraq and Afghanistan," the three-judge appeals panel wrote in September 2008.

The Justice Department had concluded that further appeal would probably be fruitless, and last month, Gibbs said the president had concurred with that conclusion, though without commenting on whether Obama would support the release if not pressed by a court case.

Thus, the administration assured a federal judge that it would turn over the material by May 28, including one batch of 21 photos and another of 23 images. The government also told the judge it was "processing for release a substantial number of other images," for a total expected to be in the hundreds.

The court also has already rejected another argument the president and his spokesman made, that the photos add little of value to the public's understanding of the issue. "This contention disregards FOIA's central purpose of furthering governmental accountability," the appeals court panel concluded in the same decision.

Obama's own Jan. 21 memorandum on honoring the Freedom of Information Act also takes a different line. "The government should not keep information confidential merely because public officials might be embarrassed by disclosure, because errors and failures might be revealed, or because of speculative or abstract fears," it said.

The president informed Gen. Ray Odierno, commander of U.S. troops in Iraq, of his decision during a White House meeting on Tuesday.

Gen. David Petraeus, the senior commander for both wars, had also weighed in against the release, as had Gen. David McKiernan, the outgoing top general in Afghanistan.

Military commanders' concerns were most intense with respect to Afghanistan. The release would coincide with the spring thaw that usually heralds the year's toughest fighting there — and as thousands of new U.S. troops head into Afghanistan's volatile south.

Defense Secretary Robert Gates said he had once held the view that it might be best to "go through the pain once" and release a large batch of images now, since so many are at issue in multiple lawsuits. But he — and the president — changed their minds when Odierno and McKiernan expressed "very great worry that release of these photographs will cost American lives," Gates said before the House Armed Services Committee.

"That's all it took for me," Gates said.