A state prison guard was fatally stabbed yesterday and three corrections officers were injured, one seriously, during fights with inmates yesterday at the Maryland State Penitentiary in Baltimore.

Corrections officials said that four inmates were injured during the violence, which they said occurred at about 3 p.m. in three separate incidents.

Authorities identified the dead guard as Herman Toulson Jr., 39, a seven-year veteran of the Maryland Department of Corrections.

Toulson, who died at about 4 p.m. at Johns Hopkins Hospital, is believed to be the first Maryland state corrections officer to be killed in the line of duty.

Corrections officials said that Willie James Newkirk, 37, a 12-year veteran of the department, was in guarded but stable condition at the University of Maryland Hospital in Baltimore with stab wounds to the left side. The other injured guards were not seriously injured and were treated at a local hospital and released.

Beverly Marable, spokeswoman for the corrections department, said that it was unclear last night whether the outbreaks, which occurred within a 10-minute period, were related.

The brief outbursts appeared to be isolated events, Marable said, and there was no large disturbance by the 1,446 inmates housed in the penitentiary, which is in the heart of Baltimore, about 15 blocks northeast of the Inner Harbor area.

Conditions at the prison late last night were tense but calm. Marable said all inmates were confined to their cells as a "lockdown" condition, in effect since shortly after the incidents, continued. She said that the cells of inmates involved in the disturbances were searched, but no general search had taken place.

"We don't want to go in and create more tension . There will probably be a shakedown soon," Marable said.

Lou Panos, spokesman for Gov. Harry Hughes, said last night he did not know whether the governor had been told of the guard's slaying but that notification would be routine in such instances.

Panos said he did not think that the violence was related to changes in the corrections department's leadership. Thomas W. Schmidt was removed as corrections head and replaced by Frank Hall about 18 months ago.

"This reflects the day-to-day operations of the prison rather than a policy" change, Panos said.

Marable said last night that no charges had been filed and the department's investigation was continuing. Baltimore City Police homicide detectives also are investigating the assaults.

Marable said that the first of yesterday's disturbances occurred at about 2:50 p.m., when Officers Toulson and Newkirk attempted to lock two prisoners in their cells after a recreation period.

She said that the inmates were housed on the fifth floor of the South Wing, which houses 382 inmates who for reasons of their own safety or the safety of others are segregated from the general population.

The two inmates, apparently armed with a homemade knife, attacked the guards. Toulson was stabbed in the abdomen and left back, and Newkirk was stabbed in the left side, Marable said.

Authorities said that several other officers immediately went to the fifth floor and subdued the inmates.

A spokesman for the Baltimore City police said that Nathaniel Appleby, 33, serving a life sentence for murder and robbery with a deadly weapon, and Andre Swann, 23, serving a 10-year sentence for robbery with a deadly weapon, were taken to the Univeristy of Maryland Hospital.

Marable said the inmates were treated for head injuries and returned to the prison.

After the guards were attacked, she said, the entire prison was "locked down," meaning that all the prisoners were confined to their cells.

Minutes later, according to Baltimore City police, as two officers were attempting to return a prisoner to his cell on the fourth floor of the South Wing, the inmate turned on the guards and began slashing at them with a sharp object believed to be a pen.

Officer Carl E. Bright, 31, was stabbed in the face and kicked in the groin, and Officer Brian Staten, 27, received back injuries when he was thrown against the cell door, Marable said. Both were treated at Mercy Hospital in Baltimore and released, a spokeswoman for the hospital said.

Additional officers soon subdued the inmate, Marable said.

Police said that inmate Kevin Thomas, 23, who is serving 6 1/2 years for assault and battery, was taken to the University of Maryland Hospital. Hospital officials said that he was in stable condition last night with multiple head and back injuries and a fractured left arm.

About five minutes after the incident on the fourth floor, police said, two inmates locked in a cell on the second floor of the South Wing began fighting for an unknown reason.

Police said that one of the inmates used a homemade knife to stab his cellmate. They said that Jeffery Jones, 35, who is serving an eight-year sentence for assault, was taken to the University of Maryland Hospital, where he was listed in stable condition. Marable said that Jones received injuries to the face, neck and chest.

William D. Wharton, an executive board member for the American Federation of State, County and Municipal Employees, the union that represents guards at the prison, said that the dead officer, Toulson, had been assigned to the segregation unit for seven years and recently had asked to be transferred because of threatening remarks allegedly made to him.