Virginia law enforcement authorities were searching a forest near Roanoke yesterday for a 31-year-old murderer-skyjacker from Northern Virginia who escaped from the state's Bland Correctional Center Wednesday night by walking past a prison guard and out an unlocked front door.

More than 100 lawmen were hunting with bloodhounds through the brush of Jefferson National Forest for Bryce Matthew Tuller, whose escape at 7:10 p.m. Wednesday was the latest in a series of breakouts that has embarrassed state officials and led to a shakeup of the state prison system.

Tuller's escape from the medium-security facility came less than a week after five inmates fled the Nottoway prison, and six months after the May breakout of six death-row prisoners at the Mecklenburg correctional facility. All were recaptured, but the escapes and other disturbances at state prisons have drawn national attention and fueled criticism of the administration of Gov. Charles S. Robb.

Neither Robb nor Allyn R. Sielaff, who became the state's chief correctional officer last week after the resignation of Robert M. Landon, had any comment yesterday on Tuller's escape, their spokesmen said.

But John Williams III, chairman of the state Board of Corrections, said he thought Tuller was too dangerous to be housed at the medium-security prison and should have been transferred to maximum-security Mecklenburg.

Tuller, convicted in 1975 with his father and brother of the 1972 murders of an Arlington policeman and and the manager of a Crystal City bank, was serving two life terms plus 15 years. The three self-proclaimed "political revolutionaries" and admirers of Cuban guerrilla Che Guevara are also under 100-year federal sentences for their role in the fatal shooting of an airline employe and hijacking of a plane from Houston to Cuba days after the Arlington murders.

Wayne J. Farrar, spokesman for the state prison system, said Bryce Tuller entered the prison mailroom in the basement of the administration building with a package containing a razor that Tuller wanted to mail back to the manufacturer.

When the guard turned around to weigh the package, Farrar said, Tuller opened the locked mailroom door with a "key or some other device," slipped past the guard through another door, which may or may not have been locked, ran up the stairs outside the mailroom and out the unlocked main front door of the prison.

Farrar said there were no guards between the mailroom and the front door, which is "never locked." "I can't explain why," he said. "Naturally, these are questions the department would like answered."

Tuller, who is considered dangerous, was wearing his own gray sweatshirt over the standard blue denim prison uniform, Farrar said. Prison officials do not believe he had a weapon or money, he added.

No prison employes have been disciplined, pending an investigation.

Tuller, his father Charles, and brother Jonathon reentered the United States on June 21, 1975, after three years in Cuba. Bryce Tuller told Arlington police at the time that the Cubans held them in solitary confinement with little to eat and forced them to labor in sugar cane fields.

Police said he told them the three were suddenly summoned June 20 by Cuban authorities who gave them $1,400 in cash, the identification papers they brought in with them and plane tickets to Jamaica. From there they went to Nassau and Miami, finally making their way to Fayetteville, N.C., where Bryce Tuller was arrested July 3 during an attempted robbery. His father and brother, accomplices in the robbery, fled to Alexandria and gave themselves up July 7.

After he returned to Arlington, police said, Bryce Tuller told them they had wanted to come home "because nothing in this country can be as bad as what we went through in Cuba."