A legendary figure in the plaintiff’s bar in new York and across the nation, Melvyn Weiss, has agreed to plead guilty to conspiring with his law partners to obstruct justice by making secret payments to plaintiffs in securities lawsuits.

As the plea agreement was filed in federal court in Los Angeles, the law firm that Mr. Weiss founded, Milberg Weiss LLP, announced that he was resigning and that the firm would now be known simply as Milberg LLP. Mr. Weiss, 72, agreed to a prison sentence of between 18 and 33 months, as well as fines and forfeitures totaling $10 million.

“I deeply regret my conduct and apologize to all those who have been affected, including all of the wonderful and extremely talented lawyers and other employees of the firm, none of whom had any involvement in any wrongdoing,” Mr. Weiss said in a written statement.

Mr. Weiss is the fourth partner or former partner at Milberg Weiss to plead guilty in the fraud scheme, which allowed the firm to file class action suits more quickly than its rivals. The firm’s lead status in those cases brought in $250 million in legal fees, prosecutors said.

A top Milberg Weiss partner who left the firm in 2004, William Lerach, was sentenced last month to two years in prison for his role in the conspiracy. Two other top lawyers at the firm, David Bershad and Steven Schulman, are awaiting sentencing.

In papers accompanying the proposed plea, Mr. Weiss admitted that the conspiracy lasted for 25 years or more. He also acknowledged that he personally paid what prosecutors called kickbacks to one plaintiff in cash and another by check.

Legal analysts said yesterday that they expect Mr. Weiss to get the maximum 33-month sentence because he was more involved in the wrongdoing than the other lawyers.

“I thought he made a strategic mistake by not settling earlier when Bill Lerach did,” a Columbia law professor who worked with Milberg Weiss on several cases, John Coffee, said. “This is a soft deal compared to what he could have gotten had he gone to trial: 20 to 30 years.”

Mr. Weiss was the last major target for prosecutors, who have been pursuing his firm for more than seven years. He was an impassioned crusader against what he viewed as pervasive wrongdoing in corporate America. He also pressed cases against Swiss and German banks on behalf of Holocaust victims.

The $10 million fine is unlikely to put much of a dent in Mr. Weiss’s overall wealth. Prosecutors said his share of firm profits from 1983 to 2005 was about $210 million. He owns a $5.7 million home in oyster Bay and a $2.7 million apartment in Boca Raton, Fla. Causes Mr. Weiss supported, such as the Israel Policy Forum and the Anti Defamation League, had no comment on yesterday’s developments.

The veteran lawyer opened his home for fund-raisers for the democratic Party and candidates such as Senator Clinton. A spokesman for Rep. Charles Rangel said the $4,600 Mr. Weiss gave last year had been donated to charity. A spokesman for Mrs. Clinton did not respond to an inquiry about the $4,600 Mr. Weiss gave to her presidential bid.

New York University said yesterday that it would consult with Mr. Weiss before deciding whether to rename the public interest programs named for the attorney and his wife, Barbara. “Clearly, he has more pressing matters to attend to,” a school spokesman, Jason Cassell, said.

Mr. Coffee said Mr. Weiss’s plea would “free the door” for Milberg to seek a settlement of the criminal charge still pending against the firm itself. The professor said strict monitoring of the firm was likely and might also involve state bar authorities. “They’ve never had a firm of this size plead guilty to what I’ll call pervasive misconduct before,” he said. As he bid farewell to his firm, Mr. Weiss said he hoped it would soldier on. “I believe that it is very important to preserve this unique legal resource for the benefit of victims of wrongdoing affecting the masses, who historically have been underserved in so many ways,” he said.