by Jeff Zeleny

President Obama is seeking to block the release of photographs depicting American military personnel abusing captives in Iraq and Afghanistan, an administration official said Wednesday.

The president's decision marks a sharp reversal from a decision made last month by the Pentagon, [1] which reached a deal with the American Civil Liberties Union to release photographs showing incidents at Abu Gharib and a half-dozen other prisons.

"Last week, the president met with his legal team and told them that he did not feel comfortable with the release of the D.O.D. photos because he believes their release would endanger our troops," said the official, speaking on condition of anonymity. "And because he believes that the national security implications of such a release have not been fully presented to the court."

Mr. Obama advised his top military commanders about his decision in a meeting on Tuesday at the White House. Several military officials had argued against the immediate release of the photographs, saying such action could harm American troops in the field.

"The president strongly believes that the release of these photos, particularly at this time, would only serve the purpose of inflaming the theaters of war, jeopardizing US forces," the official said, "and making our job more difficult in places like Iraq and Afghanistan."

"Odierno and McKiernan and Petraeus have all voiced real concern about this," said Geoff Morrell, the Pentagon press secretary. "Particularly in Afghanistan, this is the last thing they need." Mr. Morrell said. Defense secretary Robert M. Gates shared the concerns of his commanders about the impact of the photo release on the troops and the battlefield and that Mr. Gates and President Obama had had a "multitude of conversations" on the issue.

The Pentagon's decision to release the pictures came after the A.C.L.U. prevailed at the Federal District Court level and before a panel of the Second Circuit. The photographs were set to be released on May 28. But as that date approached, a growing sense of unease among military officials was expressed to the White House.

Many also recalled the Abu Ghraib photographs, showing prisoners naked or in degrading positions, sometimes with Americans posing smugly nearby, caused an uproar in the Arab world and concerns within the military that the actions of a relatively few service members had tainted the entire forces.

In this more recent case, the A.C.L.U. argued that disclosing the pictures was "critical for helping the public understand the scope and scale of prisoner abuse as well as for holding senior officials accountable for authorizing or permitting such abuse," said Amrit Singh, who argued the case on behalf of the group before the United States Court of Appeals for the Second Circuit, in Manhattan.

A senior administration official said that the president met last week with his legal team and reached the conclusion that the interests of the military and the U.S. government would not be served by releasing the photos.

"The president would be the last to excuse the actions depicted in these photos," the administration official said. "That is why the Department of Defense investigated these cases, and why individuals have been punished through prison sentences, discharges, and a range of other punitive measures."

The next step was not immediately clear. White House officials said a court filing was due on Wednesday, which would outline the administration's legal approach.

Robert Gibbs, the White House press secretary, is set to take questions about the photographs during the press briefing that is scheduled for 1:30 p.m.

During the court case, defense officials had fought the release of the photographs, connected with investigations between 2003 and 2006, on the grounds that the release could endanger American military personnel overseas and that the privacy of detainees would be violated. But the Second Circuit, in upholding a lower court ruling, said the public interest involved in release of the pictures outweighed a vague, speculative fear of danger to the American military or violation of the detainees' privacy.

Earlier reports indicated that at least some of the new pictures show detainees being intimidated by American soldiers, sometimes at gunpoint, but A.C.L.U. officials said last month it was unclear what scenes were captured. At the lower court phase, a federal prosecutor said the Pentagon had agreed to release 44 photographs involved in the case, plus "a substantial number of other images" gathered by Army investigators.