After hearing Fairfax County Sheriff James D. Swinson admit yesterday that "some mistakes" were made in the treatment of an inmate who died after confinement in the county jail, the Fairfax County Board of Supervisors unanimously called for a detailed independent study of the way the jail is run.

The board voted for the study following Swinson's statement and a detailed presentation by Commonwealth's Attorney Robert F. Horan Jr. on the events surrounding the Dec. 8 death of 28-year-old construction worker Donald L. Ferguson.

"In my opinion," Horan said, "there was a failure to monitor (Ferguson's) situation in the jail during the time he was virtually unable to take care of himself."

Horan, who was asked by the supervisors to look into the death, said that Ferguson was not treated in accord with the jail's own rules and that "I'm sure there will probably be a civil suit in this incident."

Ferguson, who was arrested for failure to pay a $50 fine for tampering with two batteries, went into acute alcohol withdrawal in the jail on the morning of Dec. 4, Horan said. The jail physician, Dr. David M. Abbott, saw the prisoner at noon and prescribed Valium, an injection of vitamin B-1 and said that restraints should be put on Ferguson, Horan said.

Horan said he found that only two shots of Valium were given Ferguson, that vitamin B-1 was not given and that sometime on Dec. 4 Ferguson was put in handcuffs and leg irons, with the handcuffs fastened behind Ferguson's back and attached to the leg irons.

"It didn't appear that he came out of that position until 6:30 a.m. two days after he was shackled, Horan told the supervisors. During that time, the prosecutor said, Ferguson had no toilet facilities and was unable to feed himself.

Horan said Ferguson died of kidney failure at Western State Hospital in Staunton, Va., where he had been taken from the Fairfax jail.

Sheriff Swinson, standing beside Horan at a podium in front of the supervisors, said the prosecutor's investigation was "thorough and accurate" and said that he welcomed an outside study of the county jail.

"It is fair to say we did make some mistakes," the sheriff said. He said the jail medic on duty was responsible for the care of Ferguson, who, in his medical condition, had become a "patient" instead of an inmate.

M. Wayne Huggins, Swinson's chief deputy, said disciplinary action would be taken against the medic who was responsible for giving Ferguson his medication and possibly other personnel who were involved in the case.

"There was negligence -- what more can you say?"

Horan told the supervisors that an attempt was made on Dec. 5 to send Ferguson to the alcohol treatment unit at Fairfax Hospital, but that the 11 beds at the hospital used for detoxification were full.

In an interview yesterday, Peggy Pond, a spokesman for the hospital, said the hospital has no record of any attempt to place Ferguson in its care. She said the 11 beds were occupied on Dec. 5, but that the hospital always will accept a patient if a "physician feels there is a need to hospitalize him."

She said the hospital does require that the jail send a sheriff's deputy to the hospital to guard the patient and that the sheriff's department is "somewhat reticent" about sending over a deputy.

Yesterday's session with Horan, Swinson and the Board of Supervisors was the second such meeting in the past six months over problems arising out of the county jail.

In August, Horan told the supervisors that there was a "widespread" pattern of inmate misuse by deputies who premitted inmates to leave the jail for conjugal visits and who used prisoners for illegal work outside the jail.

A study of jail operations was proposed at that time but not acted upon.

Ferguson was the third black inmate in the past five months to die after staying in the jail. staying in the jail.