A 25-year-old dishwasher pleaded guilty in Montgomery County Circuit Court yesterday to first-degree murder in the fatal shooting of the manager of O'Brien's Pit Barbeque restaurant in Rockville during a holdup there last fall.

Raymond Latour Offutt of Rockville also pleaded guilty to two counts of armed robbery, two of using a handgun to commit a crime, conspiracy to commit robbery, burglary and felony theft. He is scheduled to be sentenced today by Judge John J. Mitchell and could be sentenced to as much as life plus 115 years in prison.

Detective Clarence Orbin testified that Offutt and Gerald Fairfax, 18, wearing masks and wielding handguns, entered the restaurant at 1314 Gude Dr. about 10 p.m. last Oct. 27. Fairfax held five employes in the rear of the restaurant while Offutt, who had worked at the restaurant for one day last summer, confronted manager Michael O'Callahan at the cash register and shot him in the head, according to testimony.

The men, who were driven to the scene by Jeremy High, 19, fled with about $1,000, $500 of which was used the next day to pay a bond to get Offutt's girlfriend out of jail.

Montgomery County police arrested the three men at separate locations the next day. Fairfax, who was charged with first-degree murder, armed robbery and illegal use of a handgun in a crime, pleaded guilty and became a government witness. High, who also became a government witness, pleaded guilty to being an accessory to armed robbery and two counts of transporting handguns. Both men are awaiting sentencing.