WASHINGTON — President Obama declared yesterday 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.

Obama's turnabout set off immediate reactions from bloggers, liberals who decried that he was buckling to political pressure and conservatives who agreed with the decision but said it proved the president was a flip-flopper.

The White House had said last month it would not oppose the release of dozens of photos from military investigations of alleged misconduct. But American commanders in the war zones 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, realizing how high emotions run on detainee treatment during the Bush administration and now, made it a point to personally explain his change of heart, stopping to address TV cameras late in the day as he left the White House for a flight to Arizona.

He said the photos already had 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 that are now 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."

The Justice Department immediately filed a notice with the court of its new position on the release, including that it was considering an appeal with the Supreme Court. The government has until June 9 to do so.