But late Thursday afternoon, Kerry began calling fellow Democratic senators, in a quixotic, last-minute effort to urge a filibuster to stop the nomination.

Democrats cringed and Republicans laughed at the awkwardness of his gesture, which almost no one in the Senate expects to succeed.

''God Bless John Kerry,'' said Don Stewart, a spokesman for Sen. John Cornyn, R-Texas, a member of the Judiciary Committee. ''He just cinched this whole nomination. With Senator Kerry, it is Christmas every day.''

Steve Schmidt, a White House spokesman working on the nomination, said Kerry's move ''says a lot less about Alito than it does about the Iowa primary in 2008,'' suggesting that Kerry, who lost the presidential race in 2004, was playing to the party's liberal base in a bid to once again seek his party's nomination.

Sen. Harry Reid, the Democratic leader, sounded almost apologetic about Kerry's move. ''No one can complain on this matter that there hasn't been sufficient time to talk about Judge Alito, pro and con,'' Reid said on the Senate floor.

Kerry's call for a filibuster was joined by his fellow Democrat from Massachusetts, Sen. Edward Kennedy.

Under Senate procedures, their objections blocked the Senate Democratic and Republican leaders from setting Tuesday as the date for a vote on confirmation. Instead, the Senate will vote Monday on the question of whether to close debate. Sixty votes are required to trigger a full vote of the Senate on Alito's confirmation. More than 60 senators have pledged to do so and Republican leaders said they expect to hold the full vote on Tuesday.