The American Civil Liberties Union, saying an "atmosphere of violence" continues to exist at Virginia's troubled Mecklenburg prison, has asked a federal court to appoint an overseer to force the state to comply with a prisoner agreement it signed with the ACLU more than 18 months ago.

The ACLU, in a brief filed before U.S. District Judge Robert R. Merhige Jr., said officials at the prison, scene of an unprecedented escape by six prisoners from death row and several inmate disturbances this year, have failed to implement 16 of 40 provisions in the 1983 agreement.

The ACLU's National Prison Project, which has battled the state for years over its prison system, charged, for example, that the Southside Virginia prison has failed to prevent excessive force by guards, refused to videotape disturbances, unduly curtailed exercise, food service and other prisoner services and refused to implement a "phase" system to allow inmates a chance to be moved from the maximum security facility.

The ACLU action, which had been expected for weeks, is the latest setback for the problem-plagued Department of Corrections where a series of inmate incidents throughout the prison system forced Gov. Charles S. Robb to accept the resignation two weeks ago of director Robert Landon.

Allyn R. Sielaff, who took over from Landon last week, already has announced sweeping changes in staffing and managment to beef up security, including the immediate hiring of 132 new guards.

Neither Robb nor Sielaff would comment on the ACLU action.

"We always let our lawyers do our talking for us in court," said corrections spokesman Wayne Farrar.

Earlier this year, Robb had suggested that the state itself might go into court to seek changes in the agreement, but was quickly told by state Attorney General Gerald L. Baliles there was no sound legal basis for that.

Robb, a special investigative panel of the state Board of Corrections, outside consultants and other state officials have since stressed that the ACLU agreement has not lessened security at Mecklenburg despite complaints by some guards critical of the ACLU.

Corrections officials acknowledged recently that they had not attempted to explain the ACLU agreement to ranking officers, guards or prisoners at Mecklenburg.

In October, in response to a separate ACLU action, Merhige issued a stinging order to the state to relax security restrictions at Mecklenburg that he said were simply "public relations gimmickry" that kept lawyers from seeing clients in the prison.

Corrections officials have still not found a replacement for Mecklenburg's warden, who was transferred after the May 31 death row escapes.

The state, which generally has been on the losing side in court cases with the ACLU, has been forced to pay more than $260,000 of the organization's legal fees in addition to the thousands of dollars spent contesting court actions initiated by the ACLU. The ACLU has pending a request for $43,000 to recover costs of an October hearing before Merhige.