WASHINGTON (Reuters) - President Barack Obama opened the door on Tuesday to possible prosecutions of U.S. officials who laid the legal groundwork for harsh interrogation of terrorism suspects during the Bush administration.

Obama also said he would not necessarily oppose an effort to pursue a “further accounting” or investigation into the Bush-era interrogation program that included waterboarding, sleep deprivation, forced nudity, shoving people into walls and other methods.

That marked a shift for the Obama administration, which has emphasized it does not want to dwell on the past with lengthy probes into policies put in place by President George W. Bush after the September 11, 2001 attacks.

But pressure in the U.S. Congress is growing for a full-blown investigation of the CIA interrogation program.

Controversy has erupted across the political spectrum over last week’s release by the Obama administration of classified memos detailing the program to question al Qaeda suspects.

Human rights groups say tactics such as waterboarding -- a form of simulated drowning -- constituted torture and violated U.S. and international laws. Conservative critics contend Obama has endangered the country by releasing CIA secrets.

The New York Times reported that Dennis Blair, Obama’s national intelligence director, told colleagues in a private memo last week that the harsh interrogation techniques yielded “high-value information” that “provided a deeper understanding” of the al Qaeda organization.

The newspaper reported that Blair sent his memo on the same day the Obama administration publicly released the Bush-era memos. It said Blair’s assessment that the interrogation methods produced important information was deleted from a condensed version of his memo released to the news media.

REPORT SAYS TACTICS SPREAD TO IRAQ

A congressional report released late on Tuesday traced how a Bush-era policy on interrogation at the U.S. detention center at Guantanamo Bay, Cuba, helped set the stage for detainee abuse at the Abu Ghraib prison in Iraq and in Afghanistan. The report may add impetus to calls for a wider probe.

The report, released by Senate Armed Services Committee Chairman Carl Levin, laid blame for the abuses on former Vice President Dick Cheney, former Defense Secretary Donald Rumsfeld, former U.S. Attorney General Alberto Gonzales and other top Bush administration officials.

“The report represents a condemnation of both the Bush administration’s interrogation policies and of senior administration officials who attempted to shift the blame for abuse -- such as that seen at Abu Ghraib, Guantanamo Bay and Afghanistan -- to low-ranking soldiers,” Levin said.

“It was senior civilian leaders who set the tone.”

President Obama walks towards Air Force One before departing Andrews Air Force Base outside Washington for an Earth Day event in Iowa, April 22, 2009. REUTERS/Larry Downing

Earlier, in an Oval Office question-and-answer session with reporters, Obama reiterated his vow not to prosecute CIA interrogators who relied in good faith on legal opinions from the Bush administration condoning the harsh methods.

However, Obama did not rule out charges against those who wrote the opinions justifying the methods used on captured terrorism suspects.

“With respect to those who formulated those legal decisions, I would say that is going to be more of a decision for the attorney general within the parameters of various laws, and I don’t want to prejudge that,” Obama said after meeting Jordan’s King Abdullah.

“I think that there are a host of very complicated issues involved there,” Obama said.

The comment seemed at odds with the position offered on Sunday by Obama’s chief of staff Rahm Emanuel, who told ABC that the president did not believe the authors of the legal opinions should be prosecuted.

White House spokesman Robert Gibbs brushed aside questions about the contradiction. “Instead of referring to what anybody might have said ... it’s important to refer to what the president said,” he said.

While human rights advocates have urged prosecutions for those involved in the interrogation program, Obama has received scathing criticism from some conservatives over the release of the memos detailing the harsh methods.

Among the most outspoken critics has been Cheney, who contends the questioning yielded valuable information about terrorist activities and has accused Obama of endangering the country by releasing the CIA memos.

But Sen. Dianne Feinstein, the Democratic head of the Senate Intelligence Committee, welcomed Obama’s comments about a possible inquiry as a “step forward.”

Feinstein has urged Obama to withhold judgment on possible prosecutions pending a closed-door review by her committee of the interrogation program.

Obama said he would not necessarily oppose a U.S. panel to investigate the interrogation program. But he said he would prefer to see such an inquiry take place outside of the “typical hearing process” of Congress, where the issue could become politicized.