Federal prosecutors are increasingly concerned about vacancies at the top of the Justice Department which Attorney General Edwin Meese III has been unable to fill for nearly a month.

U.S. attorneys held a lengthy discussion about the vacancy in the department's No. 2 post, concluding in an informal vote that they want one of their colleagues, rather than someone from outside the department, to fill the position, said three department sources, speaking on condition of anonymity.The consensus at Tuesday's meeting at the Justice Department was that Robert Ulrich, the U.S. attorney in Kansas City, should be chosen by Meese to become deputy attorney general, said the sources.

Ulrich is chairman of the U.S. attorneys' advisory committee but was not in the room at the time of the discussion by the panel's 15 or so members, said the sources.

The post of deputy attorney general became vacant last Friday with the departure of Arnold Burns, who resigned March 29, telling colleagues Meese's refusal to resign in the face of a nearly yearlong criminal investigation was damaging Justice Department operations. Criminal division chief William Weld resigned with Burns for similar reasons.

The concerns by U.S. attorneys about the top-level Justice Department vacancies come amid a report that a group of President Reagan's advisers and friends have joined forces to oust Meese.

Reagan reacted heatedly when reporters queried him about the Wall Street Journal report, which said Nancy Reagan supported the effort.

"I thought the story was totally inaccurate," said Reagan, who when asked what might prompt him to get rid of Meese, said: "Well, if he had a complete change of character."

The office of deputy attorney general is vital to the effective functioning of the 93 U.S. attorneys' offices. The deputy makes key budget decisions that affect the offices and settles disputes between them.

The advisory committee is an administrative group that keeps the attorney general in touch with the various U.S. attorneys' offices.