Special counsel Robert Mueller speaks to reporters in late May at the Justice Department in Washington. House Republicans are pledging tough questioning of Mueller when he testifies before Congress this week, and Democrats plan to air evidence of wrongdoing by President Trump. Carolyn Kaster/Associated Press, file

WASHINGTON — The Justice Department instructed former special counsel Robert Mueller in a letter Monday not to answer a wide variety of questions about his investigation of the president and Russian interference in the 2016 election – a fresh indication of how difficult it may be to extract any new information or insights about the high-profile investigation when he testifies to Congress on Wednesday.

Associate Deputy Attorney General Bradley Weinsheimer said in Monday’s letter that he was responding to a request earlier this month from Mueller for guidance on how to handle questions “concerning privilege or other legal bars applicable to potential testimony in connection with” subpoenas for Mueller’s congressional testimony.

The letter also notes that Mueller had resisted testifying and that “the Department agrees with your stated position that your testimony should be unnecessary under the circumstances.”

Weinsheimer then went on to spell out the categories of information that should be off-limits in Mueller’s testimony on Wednesday before two House committees.

The Justice Department expects that Mueller will “not go beyond” the public version of his March report of his findings.

“Please note there should be no testimony concerning the redacted portions of the public version of your report,” the letter said, and reminded Mueller that the prosecution of Trump adviser Roger Stone and a separate case are still awaiting trial, “and local court rules and specific orders issued in those cases substantially restrict the Department’s ability to make public statements about those cases.”

“In addition, it is the Department’s longstanding policy not to discuss the conduct of uncharged third-parties,” the letter continued. “Established Department policy also precludes any comment on the facts developed and legal conclusions by the Special Counsel’s Office with respect to uncharged individuals, other than information contained within the portions of your report that already have been made public.”

The final portion of the letter makes a broader, vaguer admonition not to discuss matters that could be covered by executive privilege – a legally and factually complicated assertion that could, in theory, cover many topics, given that Mueller’s task was to investigate President Trump while working in the executive branch.

The letter defines potential executive-privilege-covered matters to include “information protected by law enforcement, deliberative process, attorney work product, and presidential communication privileges. These privileges would include discussion about investigative steps or decisions made during your investigation not otherwise described in the public version of your report.”

The letter instructs Mueller to decline to discuss “potentially privileged matters” so that Justice Department lawyers can review the specific topics later and decide whether they are covered by executive privilege.

Earlier in the day, a spokesman for the former special counsel said Mueller does not intend to stray beyond what was detailed in his 448-page report.

Mueller, in fact, plans to submit the publicly available version of his report on Russian interference in the 2016 election as a statement for the record, the spokesman said.

“His official statement for the record will be the Mueller report itself,” said Jim Popkin of the Seven Oaks Media Group, who was recently tapped to help Mueller handle media inquiries in advance of his congressional testimony.

Asked whether Mueller intended to speak beyond his report, Popkin referred to a May news conference in which Mueller said he would not and added: “As he made pretty clear then, you can expect him to stick pretty close to the four walls of the report come Wednesday.”

Mueller will first appear before the House Judiciary Committee starting at 8:30 a.m. Wednesday. Because of the committee’s size, that hearing is expected to last about three hours. He will then appear before the House Intelligence Committee at noon, in a hearing that is expected to last about two hours.

Popkin said Mueller will read an opening statement in addition to submitting his full report for the record. He said Mueller has been preparing for the testimony in unused office space at the WilmerHale law firm, where Mueller worked before leaving to lead the special counsel investigation.

Popkin declined to provide details of the preparation, except to say, “He’s going to be prepared on Wednesday.”

It is unclear whether lawmakers will be able to pry from Mueller any revelations. Democrats have signaled that they intend to focus much of their questioning on the episodes Mueller outlined in his report in which Trump sought to impede the investigation. Republicans, meanwhile, are likely to focus on what they see as bias among some on Mueller’s team.

Though Mueller, a former FBI director, has vast experience at congressional hearings, his testimony Wednesday probably will be more contentious than his previous appearances on Capitol Hill. Those who know him say they expect him to stick to the script and probably leave lawmakers of both parties disappointed. Mueller said at the May news conference that he hoped that event would be his last time speaking publicly about his work and that, if pressed to testify, he would not speak beyond his report.

“We chose those words carefully,” he said, “and the work speaks for itself.”