Sen. Robert G. Torricelli (D-N.J.), his support eroding rapidly over his ethics violations, unexpectedly pulled out of his race for reelection today, clearing the way for state officials to name another candidate as early as Tuesday for what has become the Democrats' most imperiled Senate seat.

"I will not be responsible for the loss of the Democratic majority in the United States Senate," an emotional and sometimes tearful Torricelli said at a packed news conference at the state capitol here late this afternoon. "I will not allow it to happen."

State party officials said they would poll the Democratic state committee overnight before naming a replacement, and Democrats said they would petition a New Jersey court to have Torricelli's name removed from the November ballot. Republicans said they would challenge the Democrats in court, arguing that under state law it is too late to replace Torricelli on the ballot, and the issue is likely to be in front of the state Supreme Court soon.

Meanwhile, Gov. James E. McGreevey (D) and other party leaders were scrambling to select a candidate with enough statewide name recognition and fundraising capacity to mount a winning race in five weeks against the Republican nominee, businessman Doug Forrester.

Rep. Robert Menendez emerged tonight as the leading choice of many party leaders to replace Torricelli, and he was weighing his options despite initial reluctance to give up his House seat and a chance to move up the leadership ladder.

Two other House members, Reps. Frank Pallone Jr. and Robert E. Andrews, also were viewed as possible candidates. Former senator Bill Bradley, who quit the Senate in 1996, told friends he had no interest in returning, while former senator Frank Lautenberg said in a statement he would "seriously consider serving again if asked."

Torricelli's move came after a Sunday night meeting with McGreevey and Sen. Jon S. Corzine (D-N.J.) and phone conversations today with Senate Majority Leader Thomas A. Daschle (D-S.D.), all of whom initially urged Torricelli to remain in the race, according to Democratic sources.

By late afternoon, Democratic strategists were contending that the decision significantly improved the party's chances of holding the New Jersey seat, which is considered vital to its hopes of retaining control of the Senate. There are 50 Democrats, 49 Republicans and one independent who votes with Democrats in the Senate, and a net shift of one seat would put Republicans back in charge.

Earlier in the year, Torricelli's seat looked safe, and in June, he held a comfortable lead over Forrester. But his position deteriorated badly over the past several weeks as he was unable to fight off the effects of the ethics scandal, for which he was "severely admonished" by the Senate last summer for taking lavish gifts from a now-imprisoned businessman and contributor, David Chang.

By Labor Day his lead had vanished, and Torricelli was hit with more bad news late last week. First, a federal judge unsealed a memo from federal prosecutors saying that investigators had found "credible" Chang's allegations that Torricelli had accepted "tens of thousands of dollars" from him in illegal gifts and cash. Then on Saturday, a Newark Star-Ledger poll by the Eagleton Institute at Rutgers University showed Forrester leading Torricelli by 47 percent to 34 percent.

One Torricelli adviser described the prosecutors' memo as "one more brick than the load could carry," and by the weekend, the senator began talking to friends and advisers about quitting the race to give Democrats a better chance of holding on to the seat.

"I could not stand the pain if any failing on my part will do damage to the things and the people that I have fought for all my life," he said, acknowledging that the campaign had become solely about his ethics and not about other issues. "I'm in a debate with a faceless foe."

There was speculation in Washington early today that Torricelli might resign his Senate seat to give Democrats a stronger legal case for replacing him on the ballot, but a Torricelli adviser said resignation was never part of the discussions. "It was one indignity too far," said another Democratic strategist familiar with the discussions.

Torricelli's Senate colleagues praised his decision. Sen. Patty Murray (Wash.), who succeeded Torricelli as head of the Democratic Senatorial Campaign Committee, said, "He put his state and party ahead of his personal ambition."

Republicans vowed to fight any attempt to put another name on the ballot, arguing that state law says no one can be replaced fewer than 51 days before an election. Forrester, speaking after Torricelli's withdrawal, said, "The laws of the state of New Jersey do not contain a 'we think we're going to lose so we get to pick someone new' clause."

Mitch Bainwol, executive director of the National Republican Senatorial Committee, said, "You can put somebody else on the ballot when somebody else has died, but political death does not qualify. He still has a pulse, which means he's still on the ballot."

McGreevey and Daschle began searching for a new candidate almost immediately after Torricelli told them he was out. Daschle called Menendez and Bradley and, according to a Democratic source, promised Menendez that the party would provide ample resources if he ran. Bradley was on an airplane much of the day and did not immediately return Daschle's call, but quickly put out the word that recruiting him was a non-starter.

Menendez attracted the interest of party leaders because of his past interest in running statewide and the potential excitement his candidacy could generate as someone who might be the first Hispanic elected to the Senate. Menendez also has about $2.5 million in his campaign fund that could be transferred to a Senate race.

Menendez was in New Jersey at a golfing fundraiser for his political action committee, but spent much of his time in conversations about the Senate race. He did not rule out running but said, "I'm here raising money for House candidates."

Pallone comes from a swing district in the state and therefore has a base in an area that will be critical to winning the election, but some Democrats fear his House seat would be put in jeopardy if he were to run for the Senate.

Democrats said that, if they succeed in their legal battle, they will have a far better chance of holding the New Jersey seat. Forrester, they said, has based his entire campaign on running against Torricelli on ethics issues and has not developed a political profile of his own. The latest Eagleton poll found that 57 percent of New Jersey voters have no clear opinion of Forrester, even though he was leading.

Torricelli was elected to the Senate in 1996, after 14 years in the House, representing northern New Jersey. Torricelli raised more than $9 million for the 1996 race, a feat that so impressed party leaders that they made him vice chairman of the Senate Democrats' campaign committee. Daschle, then the minority leader, named Torricelli chairman for the 2000 election. At the time, Republicans held a 10-vote margin in the Senate, and Democrats had to win five Republican seats to pull even -- then deemed an impossible task.

But Torricelli's unrelenting pursuit of money for the Democrats broke all records, and Democrats emerged with a 50-50 Senate. When Sen. James M. Jeffords (Vt.) left the Republican Party to become an independent, the Democrats took the majority and Torricelli was given much of the credit.

Even in his heyday, Torricelli was not a popular politician; colleagues say he specialized in being needed more than wanted. As his support plunged, Torricelli remained resolute that he could win by appealing to New Jersey's strong Democratic tendencies -- warning that without him, the Senate would fall into GOP hands.

"Bill Clinton had worse problems than this, and he came back," he told a fundraiser, according to a source. The fundraiser replied, "But Bob, people liked Clinton."

Today at his news conference, Torricelli recounted his long political career and said he would remember it fondly despite the way it ended. "Don't feel badly for me," he said. "I changed people's lives. I'm proud of every day of it, and I wouldn't change a bit of it."

His support eroding over ethics violations, Sen. Robert G. Torricelli (D-N.J.) announces his decision to drop out of the race for reelection. Gov. James E. McGreevey, at right, was seeking a new candidate.