Moving decisively to prevent bias in future research reports, the regulatory settlement announced yesterday bars Sanford I. Weill, chairman of Citigroup, and other senior officers from talking to Citigroup's research analysts on investment banking matters without a company lawyer present.

By highlighting Citigroup executives, regulators and prosecutors demonstrated their determination to stymie conflicts of interest within the investment bank's sprawling operations.

The restrictions, which Citigroup officials agreed to, are also the legacy of an unorthodox campaign by Mr. Weill, spelled out in previously undisclosed detail, to persuade Jack B. Grubman, his star telecommunications analyst, to change his rating on AT&T's stock from neutral to positive. Mr. Grubman had a neutral rating — Wall Street code for negative — on the stock from 1995 to November 1999, at which time he issued a new report with a positive rating.

While Mr. Weill has publicly acknowledged asking Mr. Grubman to take a fresh look at AT&T, documents released yesterday show that their discussions were intricate and numerous and dated as far back as the fall of 1998.

Mr. Weill accompanied Mr. Grubman to meetings with C. Michael Armstrong, then the chief executive of AT&T, and asked that Mr. Grubman's AT&T report be sent to him, before its publication, e-mail messages show.

Such a close interaction with an analyst is unusual and might open Mr. Weill and other Citigroup executives to future claims by regulators that they failed to supervise Mr. Grubman, legal experts say — even though Mr. Grubman never reported directly to Mr. Weill.

"The AT&T matter could be pertinent in a failure-to-supervise case, given the interaction between Mr. Weill and Mr. Grubman," said Robert G. Heim, a former Securities and Exchange Commission lawyer now at Meyers & Heim. "If Mr. Weill was aware that Mr. Grubman was basing his recommendations on investment banking considerations, that may make Mr. Weill vulnerable."

Regulators say that a failure-to-supervise complaint is unlikely to be brought solely on the AT&T episode. They do say, though, that it could be used as a relevant example in proving a broader case that Mr. Weill and other senior executives failed, individually, to adequately supervise Mr. Grubman.

Citigroup lawyers contend that Mr. Weill thought all along that Mr. Grubman was simply doing his job, as an objective and well-regarded industry analyst, in reassessing AT&T's performance and that he did not allow Citigroup's relationship with the company to influence his thinking.

"Based upon my knowledge of the record, in the unanimous determination of all regulators, it is unimaginable to me that any supervisory case be brought against Mr. Weill on AT&T or anything else," said Martin Lipton, a founding partner at Wachtell, Lipton, Rosen & Katz and the chief lawyer representing Mr. Weill in the discussions with regulators.

The New York attorney general, Eliot Spitzer, has himself lent credence to that interpretation, saying that Mr. Weill pushed so hard for Mr. Grubman to upgrade AT&T because as a board member and a friend of Mr. Armstrong, he had become a true believer in the company and had even bought the stock himself.

Regulators are using the word "fraud" in claiming that Citigroup issued biased ratings on some stocks in the late 1990's, a finding that civil lawyers are sure to pounce on in pursuing arbitrations and class-action lawsuits on behalf of investors.

But by paying $400 million in fines and payments as part of a larger $1.4 billion settlement with 10 Wall Street firms, Citigroup as a firm can no longer be investigated on banking and research conflicts that occurred from 1999 to 2001.

Individuals at the bank, from analysts up to Mr. Weill, received no such protection.

In a statement released yesterday, Mr. Weill apologized for past business practices and announced that Sallie Krawcheck, the chief executive of Smith Barney, which is now Citigroup's research and brokerage arm, would meet privately with the Citigroup board's compensation, audit and governance committees to review compensation and budget issues for her research division.

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