Virginia Gov. Charles S. Robb, bowing to pressure from Fairfax County officials angry about escapes and alleged mismanagement at state prison Camp 30, announced yesterday that the troubled facility will be changed to a minimum-security prison and that many of its inmates will be transferred elsewhere.

Camp 30, which has been a medium- and minimum-security prison with inmates ranging from petty thieves to first-degree murderers, will have within weeks only minimum-security inmates or inmates within eight months of being released, prison officials said.

The facility, located two miles from Fair Oaks Mall, no longer will house prisoners convicted of violent crimes, officials said, and the changes will result in the transfer of 75 to 100 of the prison's 160 inmates.

"Well that's beautiful, that is magnificent," said Fairfax County Commonwealth Attorney Robert F. Horan Jr., who has been among those criticizing the camp in recent weeks. "I can't believe they didn't do that 10 years ago."

The changes were outlined in a letter from Robb to Fairfax Board Chairman John F. Herrity, and were discussed at a meeting yesterday between corrections and county officials. County supervisors Monday demanded that the state improve security at the prison and ultimately close it.

Dave Smith, superintendent of the camp, said administrative work necessary to implement the changes had already begun, and the transfer of prisoners would begin Monday and could take several weeks to complete.

Among other changes ordered by Robb:

*Highway road crews from the camp, some of which have been supervised by unarmed highway employes and which have been a common source of escapes, will all be guarded by armed corrections officers.

*Prisoners convicted of murder, armed robbery or violent sex offenses will not be held at the camp, nor will inmates who have escaped elsewhere or are awaiting trial on other charges.

The moves by Robb may defuse what some Republicans saw as a potentially damaging political issue for the Democrats in this fall's gubernatorial campaign. Management of the prison has become a political issue, with Republicans charging that Robb's Democratic administration was responsible for the problems at the camp.

"That's fine, it's good that we finally got their attention" said Herrity, a Republican, who has been at the forefront of the camp's critics. "This would not have happened without me getting their attention," he said. "You can call it political, or whatever you want . . . . Frequently, the only time you can get someone to listen to you is in the context of a political campaign."

In his letter, Robb seemed to hint that the prison might eventually be closed, as the Fairfax supervisors have demanded.

"I now look forward to working with you and the board on the longer-term questions involved in a possible change in mission, or phasing down, of Unit #30 and the commensurate need for replacement beds in Northern Virginia to house inmates from this area," Robb said.

Neither Andrew Fogarty, state secretary of transportation and public safety, or Allyn R. Sielaff, director of corrections, could be reached for comment, and a spokesman for Robb declined to amplify on the letter.

The prison camp is located on West Ox Road in one of the most rapidly developing parts of the county. It had eight escapes in the past year, more than any other prison of its kind in the state.

Smith, who has been superintendent of Camp 30 since mid-May, said he, too, welcomed the changes ordered by Robb. "I think it's a good move . . . . I think it's something that needed to be done due to the location of the institution and the community concerns."

No final agreement emerged from yesterday's meeting between county and corrections officials about what procedures will be followed after escapes, but officials from both sides said an agreement was close at hand.

County officials have complained that citizens and local police are not promptly informed when escapes do occur, and have sought a written agreement from the state outlining notification procedures.

Jerry Kramer, a former camp inmate, met for an hour yesterday with state investigators to tell how he and another inmate were let out of Camp 30 last year "to make a midnight requisition" of materials for a building project at the prison.

Kramer, whose allegations were first disclosed in The Washington Post this week, said he and the other inmate took highway department materials to build a visitors building.