The U.S. Senate begins confirmation hearings for President Bush's nominee to lead the Central Intelligence Agency, General Michael Hayden, who currently serves as deputy director of national intelligence. Senators are expected to ask Hayden tough questions about controversial surveillance activities of the National Security Agency, which he once led.

The hearings before the Senate Intelligence Committee come amid controversy over the National Security Agency's domestic surveillance activities.

At issue is a program once led by General Hayden in which the N.S.A. eavesdrops - without warrants - on international phone calls between people in the United States and suspected terrorists overseas.

Some lawmakers have questioned the legality of the program, which bypasses a special federal court whose approval is required under law for domestic wiretapping operations.

Recent news reports have said the N.S.A. also has been collecting the domestic telephone records of tens of millions of American homes and businesses for massive databases that can be searched for clues about terror threats.

A number of lawmakers have expressed concern the alleged program may violate the U.S. Constitution's Fourth Amendment guarantees against unreasonable search and seizure.

The Bush administration is not confirming the existence of that program, saying only that intelligence activities are conducted lawfully.

Senate Majority Leader Bill Frist, a Tennessee Republican, predicts the N.S.A.'s surveillance activities will dominate confirmation proceedings for General Hayden. "The Intelligence Committee hearings will almost certainly go to the heart of the issue surrounding surveillance," he said.

The administration has briefed leading members of the House and Senate Intelligence Committees about N.S.A. activities. But Democrats on the panels have been pressing the administration for weeks to provide the information to all committee members, arguing that not doing so violates the 1947 National Security Act.

The administration bowed to the demand Wednesday, sending N.S.A. Director, Lieutenant General Keith Alexander, to brief the full committees in closed session. "It became apparent that in order to have a fully informed confirmation on the nomination of General Michael Hayden to become the new director of the CIA, all members of my committee needed to know the full width and breadth of the President's terrorist surveillance program," said Senator Pat Roberts, a Kansas Republican, who is chairman of the Senate Intelligence Committee.

The top Democrat in the Senate, Senator Harry Reid, said he hopes the confirmation hearings deal with matters besides N.S.A. surveillance, such as airline and port security. "There are so many things that need to be looked at as we look at homeland security, and hopefully General Hayden could give us some direction in that regard. His responsibilities as head of the CIA if he is confirmed are much wider than the domestic spying that he led," he said.

Thursday's hearing will begin in open session and then move behind closed doors to discuss classified matters.

Despite the controversy over the N.S.A. surveillance activities, Majority Leader Frist predicts Hayden will be confirmed as C.I.A. Director as early as next week. "He is a man with 20 years of experience in intelligence, he is a man who is known as a reformer, he is a man who is known as a strategic thinker, a man for me who is just ideal for this point in time," he said.

If confirmed, Hayden would succeed Porter Goss, who resigned earlier this month after stormy tenure marked by the departure of high level intelligence officers.