President Bush's CIA director-nominee, Gen. Michael Hayden, to face what undoubtedly will be the toughest public questioning of his 37-year government career at a Senate confirmation hearing.

CIA Director nominee Gen. Michael Hayden, right, walks with Sen. Rick Santorum, R-Pa., left, to a meeting on Capitol Hill Tuesday, May 16, 2006. [AP]

Hayden is at the center of the debate over the Bush administration's controversial domestic surveillance programs, which allowed the National Security Agency under Hayden's leadership to eavesdrop without warrants on telephone calls when one party was overseas and suspected of terrorism.

His reception by the Senate Intelligence Committee on Thursday was expected to be much different than a year ago, when the panel approved him unanimously to be the nation's first principal deputy director of national intelligence.

"I was actually delighted when you were appointed," the Intelligence Committee's top Democrat, West Virginia Sen. Jay Rockefeller, told Hayden in April 2005.

This time, Rockefeller wrote Hayden on Wednesday to lay out concerns regarding the general's independence from the administration, given his aggressive defense of the decision to conduct the warrantless monitoring.

"It is of the utmost importance that officials of the intelligence community avoid even the appearance of politicization, and that its senior leaders set an example," wrote Rockefeller, who will miss Hayden's hearing while recovering from back surgery.

He said he hoped Hayden would explain how he planned to repair the CIA, which is struggling to find its footing after a 2004 overhaul law that reorganized the U.S. spy community. Rockefeller wants to be sure the Pentagon and CIA are adequately coordinating their classic spy operations.

Some have questioned whether it is appropriate to have someone like Hayden, with his lengthy resume in military intelligence, directing the civilian spies at the CIA at a time when the intelligence community is increasingly dominated by the Pentagon. In closed door meetings with senators, Hayden, 61, indicated a willingness to retire from the Air Force if necessary.

Republicans generally have praised Hayden. "I don't think he'll be under the thumb of the Defense Department," said Sen. Orrin Hatch, R-Utah, adding that Hayden brings a tremendous intelligence background to the job.

Much of the hearing was expected to focus on a recent newspaper report that the NSA was able to analyze the calling records of millions of ordinary Americans.

Sen. Carl Levin, D-Mich., said there were serious privacy concerns. If the government maintains a database of Americans' calls, he said, "that has got to be addressed." Levin and other Democrats have not said publicly yet whether they will support Hayden, waiting to see how he handled himself in Thursday's open and closed committee hearings.

To help smooth Hayden's path, the administration reversed course after five months and decided this week to provide more information to Congress about the ultra-secret NSA's activities. That includes full briefings for the House and Senate Intelligence Committees.

Senate Intelligence Committee Chairman Pat Roberts, R-Kan., who supports Hayden, said the information was necessary to have a fully informed confirmation hearing.

"This issue will be central to the committee's deliberations on General Hayden's nomination," Roberts said, "and there was no way we could fulfill our collective constitutional responsibilities without that knowledge."

President Bush chose Hayden as CIA director-nominee after consultation with Hayden's current boss, National Intelligence Director John Negroponte. Outgoing CIA Director Porter Goss announced his retirement earlier this month after disputes with Hayden and Negroponte about the CIA's direction.