Washington ? In an exchange of speeches that increasingly focused on presidential powers and whether President Bush had exceeded them, the Senate on Wednesday began formal debate on the nomination of Judge Samuel A. Alito Jr. to the Supreme Court.

No firm date has been set for a Senate vote, although both Democrats and Republicans say they expect it to be before the president’s State of the Union address on Tuesday.

With no Democratic filibuster anticipated, Alito’s confirmation on a largely party-line vote appears all but certain; almost all of the Senate’s 55 Republicans and at least one Democrat, Ben Nelson of Nebraska, either have announced their support for him or are expected to do so.

As a result, the debate over his nomination is increasingly serving as a showcase for another controversy: warrantless eavesdropping on individuals in the United States.

“The reason presidential power issues have come to dominate this confirmation process is that we have clearly arrived now at a crucial juncture in our nation, and on our highest court, over the question of whether a president of the United States is above the law,” said Sen. Patrick J. Leahy of Vermont, the top Democrat on the Judiciary Committee.

In their Senate floor speeches, Democrats repeatedly complained that as a federal appellate judge, Alito has appeared to defer to executive authority to such a degree that they fear he will acquiesce to presidential claims of expanded powers.

Republicans accused Democrats of “smearing” Alito and unfairly representing his views.

The Judiciary Committee chairman, Sen. Arlen Specter, R-Pa., has scheduled hearings on the administration’s warrantless eavesdropping for Feb. 6. Atty. Gen. Alberto R. Gonzales is scheduled to testify for a full day.

Democrats asked Specter to add other current and former administration officials to the roster for the hearing.

“I have nothing but praise for Sen. Specter for having these hearings and trying to get to the bottom of it. I’m just worried, if it’s only the attorney general and then some academic experts, we won’t get to the bottom of it,” said Sen. Charles Schumer, D-N.Y., a member of the Judiciary Committee.

Meanwhile, Democrats on the Select Committee on Intelligence sent the committee chairman a letter demanding that he schedule a hearing on the wiretapping issue. The letter prompted a rapid and increasingly uncivil exchange between the committee’s chairman, Republican Sen. Pat Roberts of Kansas, and its top Democrat, Sen. John D. Rockefeller IV of West Virginia, over whether and how the intelligence committee should review the controversy.

Roberts insisted that he had already scheduled a briefing for members and put the issue on the committee’s agenda for discussion on Feb. 16.

Rockefeller responded that he and other committee Democrats had first requested a hearing five weeks ago and that anything less than a full hearing was too little too late.