WASHINGTON – The South Dakota Republican who defeated a former minority leader of the Senate by focusing on his efforts to block President Bush’s past judicial nominees warned his Democratic colleagues yesterday that they would meet a similar fate if they move to block Supreme Court nominee Samuel Alito.

Senator Thune’s successful campaign against Senator Daschle focused on the effort of Democrats in the Senate to block several of Mr. Bush’s nominees to the federal Court of Appeals through filibusters. With top Democrats saying in recent days that the filibuster is on the table for Judge Alito, Mr. Thune suggested that they look to his race for guidance.

“The constant message that I delivered back home was that these obstructionist tactics, particularly with respect to judges, undermines the Senate’s ability to get its work done and for us to get people confirmed to the bench,” Mr. Thune said. “So I think if you’re a redstate Democrat, you’re taking a great risk by going along with a filibuster.”

Mr. Thune’s comments came one day after three top Democrats delivered floor speeches in the Senate outlining concerns about Judge Alito and the same day that a coalition of liberal activist groups launched a series of television ads aimed at tarring Judge Alito as an enemy of minorities and civil liberties. Members of the coalition met yesterday afternoon with the Senate minority leader, Senator Reid of Nevada, to discuss strategy.

The liberal coalition, independentcourt.org, planned commercials beginning today that will air on national cable news programs and on local broadcasts in Maine and Rhode Island. The two local broadcasts are aimed at influencing three liberal Republican senators: Senators Snowe and Collins, both of Maine, and Senator Chafee of Rhode Island. Republicans could afford to lose four senators and still confirm Judge Alito by a simple majority.

A conservative group, Committee for Justice, shot back at the liberal ads by announcing that it will run 4,400 ads of its own in seven states that voted for President Bush last year but that are home to at least one Democratic senator. The ads, which focus not on Judge Alito but on the coalition that has formed to oppose him, prompted a battle of the interest groups yesterday, with one member of the liberal coalition, People for the American Way, issuing a press release blasting the conservative campaign.

“Our strategy, which is no secret, is to drive a wedge between the red state Democrats and the rest of the Democratic caucus and, ultimately, between the entire Democratic caucus and the liberal interest groups,” the executive director of Committee for Justice, Sean Rushton, said. “We want to make any association with People for the American Way and their allies, who have been so successful at setting the terms of this debate, toxic to senatorial candidates from any state other than California and New York.”

Activists on both sides of the nomination were inflamed this week with the emergence of a 1985 document in which Judge Alito, in applying for a promotion at the Department of Justice, professed to being a committed conservative. Judge Alito said in the application that he did not view the Constitution as granting a right to abortion and that he was proud to argue against quotas. Democratic senators have said that Judge Alito’s statement about abortion constitutes a legal position and is thus open game during his hearing, which is set to begin January 9.

In order to block a vote on Judge Alito, no more than five of the 44 Democrats and one Independent in the Senate could defect from the ranks. If the Democrats find the votes for a filibuster, Republicans could lose no more than five of their own in implementing a rule change commonly referred to as the “nuclear” option to end a filibuster on judicial nominees. In a sign that Democrats will have trouble mustering the votes for a filibuster, Senator Nelson, a Democrat of Nebraska, wrote an opinion piece in the Omaha World Herald yesterday calling for an up-or-down vote.

Another Democrat, Senator Lieberman, of Connecticut, told The New York Sun that he is not inclined to block Judge Alito. “It’s on the table, sure,” Mr. Lieberman said. “But I’m not forward leaning toward it.”

As interest groups battled, Judge Alito continued his rounds on Capitol Hill yesterday. Senator Clinton, Democrat of New York, met with Judge Alito in the morning and did not speak with reporters afterward. Asked while walking onto an elevator after a Senate vote how the meeting went, Senator Clinton said, as the doors closed: “We had a very good conversation, and that’s all I’m going to say. It was a private conversation, and I’m going to keep it that way.”