Lorton reformatory inmates who set fires that damaged 14 buildings there last week have said they intended to create a relatively minor incident to endorse a consultant's report predicting that prison overcrowding would lead to serious disorders, a high-ranking corrections department source said yesterday.

Although they intended to do no serious damage, they have told investigators, they soon lost control of the incident.

Prison informants have told corrections officers that "a number of people did have it Thursday's disturbance organized to coincide at a certain time," but that a "mob mentality" took over, resulting in uncontrollable fires, the source said.

The preliminary interviews by corrections officers and D.C. police were conducted before the Justice Department formed a special permanent task force to probe criminal activity at the city-run prison complex in southeastern Fairfax County. The task force of prosecutors and FBI agents has now taken over the investigation and is interviewing prisoners about the disturbance.

The disturbance at the prison's Occoquan I and II facilities caused a massive dislocation of inmates, hundreds of whom were transferred to the D.C. Jail, pushing the population there on Friday to about 1,890 inmates, almost 200 over the court-imposed ceiling of 1,694.

The population dropped below the cap at 1:35 a.m. yesterday and was 1,651 at 7:30 a.m. Under the court order for the jail, had the population stayed above the cap for more than 48 hours, the facility could have been closed to new admissions.

Mayor Marion Barry flew by helicopter yesterday morning to the prison complex for a two-hour tour of the Occoquan facilities. Barry, accompanied by 10 city officials, talked with inmates and checked on the progress of repairs.

The city has yet to release an estimate of damage, but officials said damage was far less extensive than originally believed and that nearly normal operations may resume in as little as a month.

A corrections department source said that although officials initially believed as many as five buildings, including three dormitories, were destroyed in the disturbance, that estimate has been revised to three buildings destroyed: a dormitory, a warehouse, and a small athletic storage building. A second dormitory was severely damaged but is probably salvageable, the source said.

More than 100 laborers have been working around the clock on repairs and have completed structural repairs on all but the destroyed and heavily damaged dormitories, the source said. Architects and construction engineers have determined that the repaired housing units are now safe and the corrections deprtment is moving forward with additional repairs.

Barry, interviewed after the tour, said the inmates' basic message to corrections officials was: "Your expert said we were supposed to riot, so we did."

According to high-ranking police and corrections officials who were involved in the initial investigation of the disturbance, inmates apparently wanted to stage a series of small fires. When corrections officers let the inmates out of their dorms for safety as smoke and fire started to spread, "the inmates just went off," with some apparently starting other fires, the sources said.

"The prisoners said they didn't intend to do serious damage to the institution. They were just trying to get more publicity for the report, trying to bolster the thing," the corrections source said.

The study by Kathryn Monaco, a New Mexico prison expert hired by the city, was released two days before the disturbance. The report, a subject of television and newspaper stories, said overcrowding at Occoquan "is so serious that it is reasonable to expect some major disturbance in the near future." It recommended that the city "immediately seek alternatives" to incarceration.

"The prisoners said, 'Look, if we start this, maybe they will go along with what she is saying,' " the corrections source said. "That report was definitely the thing that did it. There's no question in anyone's mind right now."

The mayor played down suggestions that the daylong uprising, in which 32 persons were injured, was sparked by overcrowding.

Barry repeated his belief that the prisoners had tried to destroy the Occoquan units.

The inmates, Barry said, have told Occoquan administrator David P. Decatur they were aware of court-ordered population caps at other city-run prisons and thought that they would be released if the housing units at Occoquan were burned down.

The city's jail-crowding emergency was staved off by the transfer of 300 inmates to the Federal Bureau of Prisons.

More than 200 other prisoners were sent to state prisons in Maryland, Virginia and Delaware, and a corrections source said yesterday that as a result of the transfers only Lorton's Central facility was above its mandated ceiling. Officials said they hoped that the population there would be under the cap by tomorrow, the source said.

Douglas Hilleboe, an attorney for inmates at the jail, said yesterday that he toured the facility Friday night when the jail population was 1,702 -- eight over the population ceiling. He said that "certainly there was some overcrowding in areas where they were holding Occoquan people." However, he said, "it was not a scene of unrest by any stretch of the imagination."

Barry toured the prisons with Decatur, James F. Palmer, the corrections department director, Hallem Williams, deputy director of the corrections department, and D.C. police chief Maurice T. Turner Jr.

Barry said investigators believe that a main fire was started in one dormitory with a series of smaller fires set afterward. Authorities originally said they believed that the fires were set simultaneously.

Sources said that at least one fire may have been started in the wooden rafters of a dormitory and threatened to spread to adjacent housing units, forcing corrections officers to release the inmates.

According to D.C. police and fire department sources, the effort to stop the fires from spreading was delayed by an argument over who was in charge between D.C. City Administrator Thomas M. Downs and Fairfax County Fire Chief Warren Isman.

Isman agreed to allow county firefighters into the institution only after Palmer intervened and "smoothed things over" with the fire chief, a source said.

D.C. Fire Chief Theodore Coleman confirmed that city fire equipment and personnel have been stationed at the prison around the clock since the fires because "Isman said there was a possibility they may not" respond to a fire at Lorton.

Coleman added that the city fire units are currently stationed at Lorton to back up Fairfax units in the event of a fire there. Coleman said Fairfax still has primary authority over firefighting operations at the prison.

A spokeswoman for Isman said that the 1984 agreement signed by him and Palmer states the agreement can be terminated in 30 days upon written notice by either party, and the "agreement is under review and termination is being considered."

However, Fairfax County executive J. Hamilton Lambert said the county is not considering ending the agreement, but is engaged in conversations with the city "relative to how the command sturcture operates" during emergencies at the prison. "I am the county executive, and the fire chief is subordinate to me," he said.

Staff writer Arthur S. Brisbane contributed to this report.