Virginia Gov. Charles S. Robb's new chief of the state's embattled prison system has built a national reputation as a liberal prison reformer, which some officials say could clash with the hardline approach of many conservative state officials.

Allyn R. Sielaff, who led prison systems in Wisconsin, Illinois and Pennsylvania, earned the support of some of the nation's most liberal prisoner advocacy groups with his educational and drug-abuse programs for inmates and his efforts to liberalize leave policies for prisoners.

"He's more towards our way of thinking than the neanderthals," said Alvin Bronstein, director of the National Prison Project, a prison watchdog group sponsored by the ACLU.

"If that is true, he will have a tough time in Virginia," said state Sen. A. Joe Canada Jr. (R-Virginia Beach), a member of the Senate Courts of Justice Committee. "We don't need a liberal for a corrections chief."

"I never characterized myself that way as a liberal ," Sielaff said in an interview yesterday. "If someone would characterize me a liberal, it would be more in the sense of program development, the humane treatment of inmates."

Sielaff, who described himself as a fiscal conservative, said he supports many alternative prison programs that would save the state money by limiting prison growth and reducing the need for new, expensive prison buildings. Sielaff said he will announce today major personnel changes in the corrections department and proposals for strengthening security in the state's prisons. Sielaff also said he will name a new warden for the maximum-security Mecklenburg Correctional Center in southern Virginia, where six death-row inmates escaped last May.

Sielaff, 53, a deputy secretary of transportation and safety for the state, becomes Robb's third corrections chief in three years. Robert M. Landon resigned last week as corrections director after a series of breakouts and inmate disturbances at the state's prisons.

Less than a week into his new job, Sielaff was faced yesterday with another escape, when a 31-year-old Northern Virginia man serving two life-sentences for first-degree murder walked out of a state prison near Roanoke Wednesday night.

Sielaff, who was strongly recruited for the job by Robb, said: "Obviously the public has lost confidence in the department. . . . We want to change its image. The way to change the image is to perform well."

The prison system in Virginia is considered one of the most politically volatile problems confronting the Robb administration. Sielaff, however, has walked into explosive political situations throughout his long career in prisons management.

He took over as chief of the Pennsylvania prisons system shortly after an inmate murdered a warden and his deputy in their prison office. He later was appointed head of the Illinois corrections department at a time when violent gang wars raged in many of the state's prisons.

"Some things he inherited and there was very little he could do," said Bronstein. "There were very difficult and turbulent times."

Sielaff, a lawyer who formerly taught criminal justice courses at an Ohio college, is described by associates in past prison jobs as intelligent, demanding and innovative.

"Prisons have been places of repression. A lot of people want it that way," said Robert L. Johnson, whom Sielaff appointed warden of Pennsylvania's largest prison. "Allyn Sielaff's position was that we had to open up those places."

During his tenure as head of the Pennsylvania corrections system in the early 1970s, Sielaff implemented liberal furlough policies for inmates despite negative publicity when a small number of prisoners did not return from their leave. He also brought more female and black employes into the corrections department.

In Pennsylvania, he is credited with implementing a system of half-way houses that gives prisoners increasing amounts of freedom in attempts to rehabilitate them. The system also allowed some prisoners to live at home part of the time. Sielaff also instituted drug-rehabilitation programs and expanded prison educational and industrial facilities in Wisconsin.

Many of those programs paralleled changes Sielaff brought to the troubled Illinois prison system. In addition, he streamlined the corrections administration, trimming the number of positions on the staff and banning private secretaries for high-ranking administrators.

Sielaff's reforms drew heavy criticism from many, including prison employe groups. "He was giving the place away," Jim Boyd, president of one Wisconsin prison employe union, said of Sielaff's programs to improve conditions of prisoners confined to solitary confinement. "I'm not sure his philosophies and policies fit in with our mold," said Boyd. He said that he and other correctional officers believed Sielaff's programs were too lenient on prisoners. "Overall, we are better off with him gone."

Del. Frank Slayton (D-Halifax), chairman of a budget subcommittee that oversees prisons, said Sielaff has a good reputation, but added that he does not know him well. Slayton, an occasional critic of the Robb administration, said Sielaff probably will do a good job of selling Robb's corrections budget to the legislators.

But, some conservative legislators are skeptical. Canada said that if Sielaff attempts to push liberal reforms, he "will create additional problems for the administration." Canada said that Virginia needs a corrections chief with a "very conservative point of view."

Administration officials say they are optimistic: "Two things strike me about Allyn," said George M. Stoddart, Robb's spokesman. "One, he's calm under fire, and two, he's bold enough to innovate . . . things that will energize the Department of Corrections."