Inmates in the Brushy Mountain State Penitentiary say they can hear the sound of the sawing at night as members of rival gangs, using everything from guitar strings to carbide jewelers' chains, try to cut their way out of their cells.

Earlier this month, the inmates say, they knew trouble was coming. The noise had gone on night after night. Black inmates on the lower level of the cage-like segregation block already had sent a warning through the prison grapevine that the noise was coming from the cells of white prisoners just above them. The word was that they planned to break out and kill blacks up on the third tier.

On the night of Feb. 8 it happened.

Seven white prisoners sawed out of their cells and, armed with a .25-cal. pistol, a switchblade and six homemade knives called "prison stickers," they took four guards hostage. Using the guards' keys, they raced up to the third level and went on a 45-minute rampage as black inmates cowered, some hiding behind mattresses, in their locked cells.

They went from cell to cell, peering in, shooting the ones they were looking for, leaving others behind, then jamming the locks to make it harder to get to the wounded.

When it was over at least 13 shots had been fired. Two of the black inmates were dead, two were wounded. The white prisoners then surrendered peacefully and released the guards unharmed.

Violence in prisons is more the rule than the exception, but the executions at Brushy Mountain have raised fears of an internal race war and questions of who controls the institution: guards or inmates.

In 1978 a Tennessee judge declared the prison system unconstitutional, citing factors including overcrowding, inadequate employment and program opportunities, poor health care and a lack of controls over inmate violence. The state is making changes, but has appealed his decision.

The killings have triggered a storm of protest from some who charge that there may have been collusion between the all-white guard force at the maximum-security institution and the white inmates who did the killing.

Last week Morgan County prosecutors said they would ask a grand jury to return first-degree murder indictments against seven white inmates. The prosecutors said they would seek the death penalty.

The Tennessee Bureau of Investigation (TBI) has begun an inquiry into the incident, and civil rights groups, including the Southern Prison Ministry, have asked the Justice Department to conduct a separate investigation.

The TBI probe already has raised serious questions. Among them:

The gun apparently was smuggled into the prison, and prison guard R.L. Potter resigned after failing a TBI lie-detector test on whether he knew anything about the weapon.

Two of the black victims and some others who are reported still to be on "hit lists" had been transferred to Brushy Mountain from Nashville just before the attack, even though there was a long history of violent clashes between those black prisoners and the white inmates involved.

The TBI also is looking into the question of why the other guards in the institution did not make an effort to rescue the four hostages. A prison medic reportedly heard the shooting and rushed to the third tier, where he confronted the white inmates.

When he asked them to give up, one of the white inmates reportedly said, "We're not done yet." The gun was reloaded and the shooting went on. After several minutes, during which no guards responded, the white inmates surrendered to the medic.

A prison spokesman explained there was a fear that the hostages would be harmed if the guards rushed into the area. He said the surrender was actually to the medic and a deputy warden.

Brushy Mountain, a massive white structure of concrete and steel, looks more like like a medieval fortress than a prison. Jinx Woods, a Nashville lawyer, describes the prison as "like walking into the mouth of hell."

The prison, built in the 1800s, is surrounded on three sides by steep mountains. Inmates get out occasionally, but a terrain of dense hardwood forests and broken limestone rocks have made permanent escape almost impossible.

Brushy Mountain has no prison industries. Authorities say they are afraid the machinery would make it even easier for the inmates to arm themselves. As a result the prisoners' lives are said to be filled with scheming, grudges and violence.

There are about 450 inmates at Brushy Mountain, about one-third of them black. For the most part they are the worst inmates in the state of Tennessee, convicted of the most horrible crimes. Prison officials say the average sentence is well over 20 years. Many inmates are serving sentences of 100 years or more. One man is in for 316 years.

The guards here are all white, and officials say that is simply because there are no blacks to hire. There is only one black family in the county. The only black employe at the prison commutes to Knoxville, nearly an hour east of here.

The economy of the rural area is entirely dependent on coal mining and the prison, where jobs are said to be handed down from father to son.

Most of the black inmates come from Memphis, in the western part of the state, a drive of about 400 miles, much of it over narrow, winding mountain roads.

"You can get from Knoxville to Detroit, Mich., before you can get from Memphis to Petros, Tenn.," said Dennie Littlejohn, the outside leader of the Alkebulan Society, a black prison organization that has gone underground at Brushy Mountain. As a result, he said, many of the blacks never have visitors.

Littlejohn and others say the isolation has contributed to serious racial tensions, including fights, stabbings and other violent incidents.

Lawyer Woods has charged that prison officials were warned ahead of time that racial trouble was about to break out and did nothing to stop it.

Her client, Barney Conley, was a close friend of the dead and wounded, and apparently escaped the attack only because he had been stabbed two days earlier and put into segregation away from the trouble area.

Conley had been transferred here less than a month before the violence, and Woods and Conley's mother had been trying desperately to have him transferred from Brushy Mountain.

In a letter to Woods just before the shootings, Conley said the prisoners "are arming up and things are getting worse . . . . Well, I am one against many now, and the outcome is already written. But I'll stand my ground and smile in their faces until the end."

Conley since has been moved to another prison.

Police had a number of theories on the motives for the shootings. One was that the whites were trying to even the score with blacks who stabbed James Earl Ray, the convicted assassin of Martin Luther King Jr., last June. Ray is a folk hero to some of the white inmates.

But there are two gangs of black inmates in the prison, those who were attacked by the white inmates and another more militant group associated with the Alkebulan Society. Three Alkebulan members have been charged with stabbing Ray.

Ray is in protective custody in Nashville.

A preliminary investigation by the TBI has concluded that the attack was not related to a racial tensions, but to a fight over control of drug distribution in the prison.

Woods said she does not believe that. "They'd only been back in the prison for two weeks. They were locked up in the segregation unit. How were they supposed to be pushing drugs?" she asked. "The real issue is who's going to control the prison. Is it going to be a faction of inmates, or is it going to be the guards?"

Mike Rothwell, associate warden for treatment at Brushy Mountain, said he believes the dispute probably involved efforts to control not only drug distribution but other criminal activities inside the prison, including protection rackets, gambling operations and homosexual prostitution.

He called the black and white gangs "groups of predatory career criminals with a history of assaultive incidents preying on weaker inmates. They'll prey blacks on blacks, whites on whites and on each other. They try this on society and they get locked up. But here you don't have the same constraints."

The black Alkebulan Society is the most militant of the gangs. Littlejohn said the group contains members of the revolutionary Black Liberation Army, but he said he is not a BLA member.

"They are very political, very dissident," he said, "but they have no guns, we have no training camp outside the walls. They consider themselves political prisoners because the crime they committed is the result of oppression of a class of people in American society. The education system has denied them the opportunity to educate themselves. The courts which convicted them were made up of all-white juries, judges and prosecuting attorneys."

Conceding that some Alkebulan members believe in violence, he said, "We refer to revolution rather than prison reform."

Rothwell said he believes the group, now underground at the prison, is very dangerous. "They have a revolutionary, terrorist philosophy. They view themselves as political prisoners of war. If they ever get out they'll kill every white person they can get their hands on."

Rothwell said the struggle among the three groups has gone on for some time. There was a major fight last April, and some prisoners were transferred to other prisons to try to avoid trouble. But, except for a small unit at the main prison in Nashville, Brushy Mountain is the only maximum-security prison in the state. Officials say the blacks were returned to Brushy Mountain after they caused trouble in other prisons.

Before the shootings there had been a number of minor incidents between the two groups involved in that incident, most involving stabbings. Rothwell said the white inmates "suspected the blacks were getting ready to hit them, so they hit them first."

There is a widespread belief at Brushy Mountain that the violence is not over. It is common knowledge that there are hit lists on both sides. The guards, who are not armed, worry that they're sitting on a volcano ready to erupt.

It is an institution where violence is a way of life, where many inmates will never get out and where weapons continue to pour in.

"We had somebody one time smuggle in a gun in a can of beans. They sew the guitar strings into the seams of their clothing. You never stop it entirely," Rothwell said.

Corrections authorities also concede that it is almost impossible to keep violent inmates segregated from one another.

Shortly after the incident, Dorothy Greer, assistant corrections commissioner, said, "We only have so many cellblocks. Certainly we make mistakes, but we don't have many choices. It's like having 10 children who all hate each other in a family. How do you keep them apart?"

Rothwell added, "We get the hard-to-manage inmates. That's the function of this institution. It's the end of the line. They're serving long sentences, they're in close confinement. You do that to a bunch of rats and they start chewing on each other. Humans are not so different."