A 19-year-old Lorton inmate, sentenced to 20 years to life in prison for the murder of a Washington restaurant owner three years ago, slipped out of the correctional facility yesterday morning under cover of a dense fog and vanished into the surrounding countryside.

Prison officials said a guard fired 14 shots at Mark Fitzgerald Roberts as he climbed over a fence and escaped from the facility's medium security unit at approximately 6:45 a.m. But investigators said they found no evidence that any of the bullets hit him.

The incident marks the first over-the-wall escape in four years for the Lorton reformatory, which this fall suffered a two-day walkout by prison guards protesting staff shortages and layoffs ordered by the District government.

An estimated 20 corrections officers and Fairfax County police officers combed the area in search of Roberts yesterday, aided by one canine unit, but had found no trace of him by nightfall. Corrections spokesmen said the search would continue, although they said they were "relatively certain" that Roberts was no longer in the Lorton area.

Roberts, who once denied in court that he was "like Al Capone" because "I only killed one person," had pleaded guilty to shooting to death the co-owner of a Chinese restaurant on South Capitol Street during an attempted robbery in March 1977. Police said Roberts also shot and crippled a restaurant worker during the same robbery attempt, but failed to get any money when the restaurant's cash register jammed.

Prison guards were quick to blame yesterday's escape on staff shortages and layoffs ordered by the District government, and said they would use the escape to mobilize support for hiring more guards. District officials earlier this week had promised to hire an additional 50 correctional officers to be spread over the district's six correctional facilities.

"We are critically short and this is the sort of thing that can happen," said Kenneth Bynum, local president-elect of the American Federation of Government Employees, who said the union is seeking at least 120 more correctional officers. "They [District government] just don't care. They think if you've got somebody up in the towers, it's enough."

Delbert Jackson, director of the D.C. Department of Corrections, yesterday acknowledged that more guards are needed at Lorton, but denied that staff shortages were to blame for the escape. "We had someone in the tower. He fired 14 shots. There is not much else you can do in a case like this," Jackson said.

According to a prison spokesman, Roberts stole out of his medium security dormitory before dawn yesterday and crept about 200 yards across an adjacent exercise field to the 10-foot fence, topped with barbed wire.

The spokesman, Douglas Stempson, said 26 correctional officers were on duty watching Lorton's 1,300 prisoners at the time, but that Roberts was not detected until he reached the top of the fence because a heavy blanket of fog covered the area.