Sen. Orrin G. Hatch (R-Utah) urged the Justice Department yesterday to conduct a full investigation of federal prosecutors' charges that the U.S. District Court Judge Robert Merhige displayed an "antigovernment bias" in his handling of the Smith-Bagley trial.

Hatch, a member of the Senate Judiciary Committee, said a special prosecutor might be needed to handle such an investigation.

The Washington Post reported last week that the two prosecutors who handled the government's case, U.S. Attorney H. M. Michaux and Assistant U.S. Attorney Patricia Lamley, had made the charges in a letter to their superior at the Justice Department.

"Somebody has to get to the bottom of this," Hatch said in an interview. "A well-known federal judge has been accused by prosecutors. I would think a federal prosecutor could get to the bottom of this."

Hatch said he will ask for Senate hearings into the charges, but emphasized that the Justice Department has "an obligation to look into this."

Hatch he would make requests for hearings and a possible investigation to Sen. Edward M. Kennedy (D-Mass.), chairman of the Judiciary Committee and Sen. Dennis DeConcini (D-Ariz.), chairman of a Senate Judiciary subcommittee.

The Office of Professional Responsibility at the Justice Department is examining allegations submitted by lawyers for Bagley that an FBI agent in the case had a conflict of interest.

That office also is looking into allegations that FBI agents and others made misstatements to a federal grand jury that handled the case.

Hatch has gone to the Senate floor twice in the last week to call attention to the charges, saying the allegations "reach to the very heart of the justice system."

Bagley was acquitted in July by a jury in Richmond of conspiracy and stock-manipulation charges. But the case has again received attention after the letter from the prosecutors became public.

Hatch said both sides' charges surrounding the case had piqued his interest in an investigation, particularly because he was an outspoken supporter of legislation that would encourage merit selection of federal judges.

Hatch said he "would like nothing better" than to have Merhige cleared of the prosecutors' allegations.

But in light of the unusual letter from the prosecutors, Hatch said he doesn't "see how the Justice Department and the Senate could ignore" the allegations.