WASHINGTON -- President George W. Bush has publicly acknowledged for the first time that someone in his administration likely leaked the identity of a CIA operative, but he said it's time to "move on."

Speaking to reporters at the White House Thursday, he said he thought his decision to spare former White House aide Lewis Libby from a prison sentence was "fair and balanced," and hoped the controversy had "run its course."

Libby was convicted of lying and obstruction of justice in an investigation of the leak.

When the controversy initially erupted, Bush said he would fire anyone discovered to have leaked Valerie Plame's identity. Deputy Secretary of State Richard Armitage eventually told investigators he may have inadvertently done it.

Bush said he has often wondered whether the matter would have disappeared had the leaker come forward earlier.

Most Americans in a recent poll said that Bush should not have commuted Libby's prison term for his role in the case.

According to a USA Today-Gallup poll, 66 percent disagreed with the president. Thirteen percent of those surveyed say the president's move was correct.

Forty-four percent of Republicans in the poll said he should not have intervened. Twenty-six percent said he did the right thing.

Libby, who was Vice President Dick Cheney's chief of staff, was the highest White House official convicted in a government scandal since the Iran-Contra affair.

The telephone poll of 1,014 adults has a margin of sampling error of plus or minus 3 percentage points. For the 394 Republicans surveyed, the margin of sampling error was plus or minus 5 percentage points.