Calm returned to Lorton Reformatory's Youth Center No. 2 yesterday after an overnight disturbance that left at least three guards and seven prisoners injured, while a political riot kicked up over how the incident was handled.

More than 100 inmates were involved in the disturbance, which began Monday night and lasted until early yesterday, according to a D.C. Department of Corrections spokesman and other department sources.

The inmates set a small fire in a dormitory and armed themselves with sticks, rocks and bricks from a construction site at the prison, according to the spokesman and sources.

Corrections spokesman Douglas W. Stempson said the inmates were returned to their dormitories yesterday morning, about seven hours after the disturbance began, after a "shakedown" search of the institution.

About 20 inmates who were "agressively involved" in the incident were tranferred to other facilities at the District-run prison complex in southern Fairfax County, Stempson said.

The incident came a week after Mayor Marion Barry and Fairfax County Board Chairman John F. Herrity signed an agreement outlining procedures the two jurisdictions would follow during disturbances or escapes at Lorton.

The agreement stopped short of spelling out when D.C. police would respond to disturbances at Lorton, and D.C. police did not respond to Monday night's incident, leaving about 40 county police officers to guard the facility's perimeter for about four hours.

Yesterday, Herrity called for another accord governing response by D.C. police to incidents at Lorton and providing for reimbursement to Fairfax when county police are used at the prison.

"For our police department to be tied up as it was for five hours is an unfair burden," said Herrity.

Herrity also called for the instigators of the disturbance to be sent to "the federal penitentiary in Afghanistan," and urged Fairfax police and prosecutors to formulate a policy statement stressing that "all force necessary, including shooting, will be used if people breach the perimeter."

Herrity acknowledged that this policy is effectively already in force, but he said: "I want to make sure everyone understands it . . . especially the prisoners."

He added: "We have some bad dudes in there, and if they got out it could cause a problem."

Barry's office declined to respond to Herrity's statements.

Stempson said Monday's disturbance began about 7:40 p.m. and was sparked by an inmate fight in a dormitory housing about 120 prisoners.

Sources said that one inmate hit another in the head with a baseball bat, and that other inmates apparently thought the injured prisoner had been stabbed because he was bleeding profusely.

About 20 inmates broke up into two rival groups, and a small scuffle ensued that spilled out into the quadrangle formed by the facility's four dormitories, according to department sources. Corrections officers separated the groups and ordered the inmates to return to their dormitory, but the inmates refused, the sources said.

Stempson said the disturbance "slowly but surely grew bigger" over the next two hours as inmates from the other dormitories went outside and joined in minor skirmishes with other prisoners. About 10 p.m., Stempson said, corrections authorities concluded that there were not enough officers in the youth center to move the inmates back to their dormitories.

Fairfax County police were notified of the disturbance at 10:10 p.m. and sent forces, including a helicopter, to patrol the perimiter of the facility.

Officers tried to persuade the inmates to return peacefully to their dormitories, sources said, but at 11:20 p.m. a small fire was set in a supply cabinet in dormitory No. 2. Ten minutes later the first volley of tear gas was fired into the yard.

Corrections officers in helmets and gas masks entered the quadrangle and were met with a shower of sticks, rocks and bricks that inmates had "stockpiled" from a construction site in the prison, according to one source. Two more volleys of tear gas were fired and the inmates were herded into the gymnasium after a 40-minute stand-off, sources said.

While the inmates were left in the gym to "cool off," Fairfax County firefighters extinguished the fire in the supply cabinet. Stempson said damage was minor. Inmates were returned to their dormitories beginning at 2:30 a.m.

Stempson said that seven inmates and three guards were injured. None of the injuries was described as serious.

An official for the American Federation of Government Employees, which represents corrections officers, complained that guards were left to face the inmates without shields or other protective equipment. Stempson defended the department's procedures as proper.

Fairfax County law enforcement officials said they have not yet computed the cost of the police response to the incident, but they assume it runs into thousands of dollars. Herrity said he would discuss the matter with Barry this week.

"It's the responsibility of the D.C. Department of Corrections to call the Metropolitan Police," said Richard A. King, deputy county executive for public safety. King said there ought to be explicit guidelines for D.C. police to be summoned to relieve county officers in major disturbances.