A federal jury in Alexandria convicted three former Lorton Reformatory inmates yesterday and acquitted three others of plotting and participating in the prison's fiery uprising last July that left 32 persons injured and one inmate dead.

The panel, deliberating for 2 1/2 hours, found Rodney Jenkins, 29, Frederick Edwards, 26, and Carl Henderson, 35, guilty of conspiracy, arson, inciting to riot, rioting and damaging government property. Michael Farrar, 28, Matthew Fogle, 30, and Kevin Metts, 24, were found not guilty.

"We are satisfied that those people primarily responsible {for the disorder} were convicted," U.S. Attorney Henry E. Hudson said after the verdict.

Testimony at the three-day trial, the culmination of an investigation by a federal task force set up in the wake of the July 10, 1986, disturbance, revealed that the uprising was meant to force the early release of some prisoners from the District-run prison's overcrowded Occoquan I and II facilities.

No such action was taken, and hundreds of Lorton residents were transferred to federal penitentiaries while 14 damaged buildings were rebuilt.

Last week, a year after the disturbance, District Department of Corrections officials began granting early releases to some Lorton residents to bring the prison population within a court-mandated ceiling.

The day before the melee broke out, The Washington Post had reported that a study by consultant Kathryn Monaco, hired by the Corrections Department, concluded that crowding was so severe that a "major disturbance" could occur "in the near future."

Early in this week's proceedings, U.S. District Judge Albert V. Bryan said he would not allow crowding "to be used as a defense" in the case and restricted defense counsel efforts to have witnesses elaborate on living conditions in the prison.

However, the 12-member jury got revealing glimpses into life inside the facility in southern Fairfax County, as well as new details about the uprising that caused $3 million in damage.

An inmate shot by guards during the disorder died from his wounds.

The jury, for example, heard that some inmates were watching an X-rated film on cable television when the first fires erupted in Occoquan's K dormitory. And an Occoquan guard testified that one of those convicted yesterday, Rodney Jenkins, had helped protect him and two other guards from prisoners armed with homemade knives.

According to testimony at the trial, 90 prisoners in K dormitory slept in one large room on each of the building's two floors. Temperatures were in the 90s and the rooms were not air conditioned.

One witness, inmate Michael Jordan, said the "dormitory was infested with flies" and, using sheets, "people had their beds set up like tents to keep the flies out."

Hudson, who has been directing the work of the Lorton task force, said "the generally uncooperative nature of inmates and the chaos which prevailed" during the outbreak made the prosecution "inherently difficult."

Since the task force's inception, more than 120 inmates have been convicted of crimes committed in the facility, Hudson said yesterday. "I think it has had an overall deterrent effect," he added. "There's far greater certainty of prosecution than ever before."

Both the government and defense cases rested on the testimony of current or former Lorton inmates allegedly involved in the uprising.

Government witnesses recounted that the first fires were set with cigarette lighters in bunks on the second floor of K dormitory, and that prisoners then began to break windows and encourage others to burn the building.

According to some prisoners who testified for the prosecution, the uprising provoked resentment among some Lorton inmates because they were moved to other federal prisons, far away from their families in the District.

One witness, Cedric Chase, testified that he overheard some of the defendants talk about calling off the disturbance hours before it occurred because "they did not have the cooperation of the masses of the jail."

Cpl. Edward Cousin, a guard at Occoquan, testified that soon after the fires in K dorm broke out, a prisoner armed with a homemade knife approached him.

Cousin, who had been called to the stand by Jenkins' attorney, said Jenkins ordered the prisoner to let Cousin and two other guards pass through the crowd to the ball field.

"I shook Mr. Jenkins' hand and thanked him for helping us to get to the ball field," Cousin testified.

Prosecutor Barry Tapp told the jury the incident revealed that Jenkins knew "the consequences would be much greater" if a guard were hurt in the uprising.

Edwards, Henderson and Jenkins, none of whom is currently incarcerated at Lorton, each face up to 51 years in prison when they are sentenced in early September.

Eight others charged in connection with the disturbance have pleaded guilty to various charges resulting from the uprising and have been sentenced.