WASHINGTON – Many of President Obama's closest advisers believe that the Sept. 11, 2001, terrorist attacks could have been prevented if the National Security Agency had possessed then its current trove of Americans' phone records.

Critics of the program disagree, and the presidential task force that reviewed surveillance operations said last month that it "was not essential" to preventing terrorism.

But as Obama finalizes a Friday speech announcing his plans to change intelligence operations, the widespread agreement among senior White House aides about the program's value appears to be driving policy.

As a result, the administration seems likely to modify, but not stop, the gathering of billions of phone call logs.

Obama has accepted the "9/11" justification, aides said, expressing the belief that domestic phone records might have helped authorities identify the men who crashed jets in New York, Washington and Pennsylvania.

He believes the main problem is perception: Many Americans don't trust the NSA to respect civil liberties.

In Friday's speech, Obama is expected to propose steps that he hopes will make Americans more comfortable with the program, but not greatly reduce its scope.

One such change would be to shift the assembling and archiving of phone "metadata" from NSA servers back to the phone companies, or to a private third party. Aides said he is unlikely to end the program altogether.

A public policy group said Monday that its review of U.S. terrorist arrests shows the government's collection of bulk phone records does little to prevent terrorism.

The nonprofit New America Foundation said it found that the program "has had no discernible impact on preventing acts of terrorism."