A federal prosecutor on Sen. John W. Warner's list of candidates to become U.S. attorney in Roanoke is facing possible disciplinary action for entering a plea-bargaining agreement that angered firearms agents in Southwest Virginia's coalfields.

The recommendation for a formal reprimand of E. Montgomery Tucker, now an assistant U.S. attorney in western Virginia, is the latest in a series of controversies surrounding the Republican senator's efforts to fill federal judgeships and prosecutor vacancies around the state.

Tucker and another assistant U.S. prosecutor, Morgan Scott, irritated U.S. Attorney John S. Edwards last month by accepting guilty pleas from two defendants accused of weapons dealing the Appalachian coalfields in exchange for sharply reduced sentences without Edwards' approval.

The two men and one of their wives were indicted in February after a months-long undercover investigation by federal agents. They faced a total of $107,000 in fines and 68 years in prison if convicted on all charges, including the illegal sale of four .38 caliber revolvers, an M16 automatic rifle and 16 other unspecified firemarms.

But after the plea-bargain, defendant Ralph Osborne of Jonesboro, Tenn., was sentenced to five years in prison with one year suspended and five years' probation. Maybelle Osborne pleaded guilty to a misdemeanor charge of marijuana possession and received a six-month suspended sentence, two years' probation and a $250 fine.

Her husband, Robert, of Lebanon, Va., is scheduled to be tried next Friday.

At a court hearing before the first sentencing Thursday in Big Stone Gap, Va., Edwards told District Judge Glen Williams, he felt obligated, "legally and morally," to support the plea arrangement.

Warner, who interviewed both Tucker and Edwards in April, said last week he had "no knowledge" of the plea bargaining incident and that Tucker had been "highly recommended to me."

"The issue is moot anyway," Warner said, because he has since told Justice he favors someone other than Tucker for the $50,100-a-year U.S. attorney's job in Roanoke.

Warner declined to say whom he prefers. Tucker was unavailable for comment and Scott declined to discuss the incident yesterday.

Edwards, who was appointed U.S. attorney by Jimmy Carter on May 14, 1980, denied the recent feud had political overtones. Both Tucker and Scott are holdovers from Edwards' Republican predecessor.

Tucker was demoted by Edwards in January from the position of first assistant U.S. attorney and repflaced by William P. Sellers IV, a move Edwards said he made simply "as a matter of internal office policy."

It was unclear whether Warner was aware of the domotion before his list of candidates was made public. Warner said he asked Tucker during an interview on April 16 in Roanoke whether there was "anything in your background that would prejudice your case" and that Tucker had said no.

Warner said he met with Edwards the same day and that Edwards had made no mention of anything detrimental about Tucker.But Edwards said he and Warner did not discuss Tucker.

Besides Tucker, Warner's candidate list includes Carroll County Commonwealth's Attorney John P. Alderman and Ray Dodson, a Wise County prosecutor and former administrative assistant to Rep. William Wampler (R-Va.). One state Republican activist, who asked not to be identified, said Alderman is the man Warner has urged Justice to pick to succeed Edwards.

Both Edwards and Dan Phelps, head of the Bureau of Alcohol, Togacco and Firemarms' Bristol office, were incensed by the plea bargain. Phelps, in an unusual move, publicly blasted the arrangement, saying it might jeopardize future investigations of weapons and drug dealing in the coalfields.

In a four-page letter to Justice, Edwards, critized Tucker's "poor judgment" in the case and said Phelps was "shocked and extremely disappointed" by Tucker's conduct.

The ATF spent more than $100,000 and 3,300 man hours in investigating the Osborne case, Edwards wrote, and he continued, "According to one of the agents, the defendants were laughing when they left the courtroom."

Edwards also charged Tucker had acted "in blatant violation of clear instructions" that plea bargains must be approved by him or his first assistant.

William P. Tyson, acting director of the executive office for U.S. attorneys, said last week no decision has been made on Edwards' recommendation for a reprimand. He declined to elaborate.

Warner's candidate list, announced June 4, was overwhelmingly white and male and drew immedaite criticism from blacks and women around Vriginia. Warner has steadfastly defended the list.