New allegations of retaliation by senior executives at the FBI have been referred to the Justice Department inspector general's office, which just completed a draft report detailing previous incidents of mistreatment against the same employee, according to FBI and congressional sources.

The incidents have renewed debate over the FBI's treatment of internal whistle-blowers, who have historically complained that the bureau's clubby atmosphere results in harsh punishment for rank-and-file workers who uncover wrongdoing.

The case also presents another challenge for reformist FBI Director Robert S. Mueller III, who has repeatedly told lawmakers that whistle-blowers will be protected even while having to deal with an increasing number of them speaking out. One of the recent incidents involves one of Mueller's handpicked senior deputies, W. Wilson Lowery Jr.

The allegations center on John E. Roberts, a unit chief who leads employee misconduct investigations in the FBI's Office of Professional Responsibility. Roberts testified in Congress last year about how his career was damaged because he helped uncover flaws in the FBI's handling of the 1992 siege at Ruby Ridge, Idaho. He repeated many of the same criticisms in a recent television interview.

His claims had already helped lead to a broad investigation of FBI personnel policies by Inspector General Glenn A. Fine. A draft report from Fine now being circulated at FBI headquarters strongly condemns top management for meting out unfair discipline, and it supports Roberts's claims of mistreatment, according to people familiar with the document.

But since Roberts appeared Oct. 27 on a "60 Minutes" television broadcast, some of Mueller's top managers humiliated and threatened him, according to his attorney and Senate investigators. The treatment came despite the fact that Roberts was preapproved to appear on the broadcast by top FBI officials, his supporters said.

"This is retaliation in its deepest form," said Kris Kolesnik, executive director of the National Whistleblower Center who is working as an investigator in Roberts's case. "The message is: Thou shalt not criticize the FBI. If you do, you're going to get hammered."

OPR officials referred questions about the incidents to the FBI press office. Lowery was traveling and did not return a telephone message left Friday. Roberts also could not be reached for comment.

FBI spokesman Michael Kortan declined to discuss any details about the case. "This matter, including the allegations in this letter, are under review by the inspector general," Kortan said.

According to a letter sent Friday to Mueller by Sens. Charles E. Grassley (R-Iowa) and Patrick J. Leahy (D-Vt.), Lowery, an executive assistant director, and Robert J. Jordan, the head of Roberts's department, "engaged in a course of retaliatory action" against Roberts that included badmouthing his performance in front of the department staff and angrily confronting him in a private meeting.

On one recent day, when Roberts was on sick leave, Jordan allegedly called an "all hands staff meeting" in which he read a transcript of Roberts's television interview and encouraged co-workers to criticize him, according to the letter. One of those at the meeting was Roberts's wife, Brenda, an FBI support employee who required medical assistance after the session was adjourned, the letter said.

The senators also allege that Lowery and Jordan called Roberts into "an aggressive and hostile conversation" in which they challenged his views and informed him that Fine's office would be asked to investigate. Jordan also allegedly told Roberts that the television appearance was "a dis" to Jordan and Mueller.

"You have repeatedly pledged -- both in public and personally to us in private -- that you do not and will not tolerate retaliation against FBI whistleblowers," Grassley and Leahy wrote in their letter to Mueller. "We urge you to follow through on these words with actions and take appropriate corrective action."

Grassley and Leahy have sponsored legislation that would beef up protections for FBI whistle-blowers, who they argue are at greater risk of retaliation than many other federal employees.

Since succeeding controversial director Louis J. Freeh last September, Mueller has had to cope with a number of high-profile cases involving proclaimed whistle-blowers. One of the most significant involved Coleen Rowley, the Minneapolis FBI legal counsel who complained that headquarters' officials stymied the efforts of local agents to search the belongings of terror suspect Zacarias Moussaoui before the Sept. 11, 2001, terror attacks.

Another case involves a former FBI wiretap translator named Sibel Edmonds, also interviewed by "60 Minutes" about her claims of incompetence and corruption in the FBI's translation services. Although Edmonds, like Roberts, had previously aired her complaints in public, her appearance on CBS prompted a formal response from FBI headquarters.

Kortan sent Edmonds a letter two days before the broadcast saying she had to get FBI approval before talking to a correspondent. Her attorney alleged that the bureau was trying to quash the interview.

"I don't know what causes them to keep making these stupid kind of moves," Kolesnik said. "They don't seem to understand the impact of their actions."