A single fan stirs the stale air in the "Adjustment Unit" at the Lorton Youth Center while two portable radios, their volumes on high, echo down the corridor.

Thirteen tiny, dimly lit cells line the corridor. Each holds two young men accused of breaking prison rules. Their punishment is to be confined here, sidestepping metal bunks, stainless steel toilets, minuscule sinks -- and each other -- for as long as prison officials feel it takes for them to learn their lesson.

Except for a daily 10-minute shower in a stall covered by a ragged cloth curtain and an occasional chance to play basketball, the 45 inmates currently held there say they must spend most of their days in their cells, cramped and all but ignored by the prison staff.

Yesterday, lawyers for the American Civil Liberties Union Prison Project and from the Washington law firm of Wilmer Cutler & Pickering filed a class action lawsuit on behalf of prisoners in the Adjustment Unit and all Youth Center inmates. The suit contends that conditions in the unit, and the procedures used to hold men there, are unconstitutional.

Incarceration in the Adjustment Unit, the lawsuit contends, "only nurtures the very hatred, violence and other forms of problem conduct that it attempts to prevent."

This is at least the third time in recent years that Lorton has been the focus of a suit pitting prisoners' rights against the prison's need to maintain discipline.

"There are times in an institutional setting when you have to isolate the disruptive element . . . so the majority of the population can benefit from the treatment and training that's provided," said Walter B. Ridley, the Youth Center's administrator, yesterday. " . . . We're not cruel people . . . We're not barbaric in any sense."

Lawyer Alan B. Sternstein of Wilmer Cutler acknowledges that the law "doesn't guarantee a prisoner the Washington Hilton." But, he said, "in the law there are certain minimum standards you have to satisfy when you put people in jail."

No money is being sought in the suit, Sternstein said. Instead, the prisoners want the court to order the District government to clean up allegedly "unhealthy and unsanitary" conditions at the Adjustment Unit and give inmates written notice and a chance to challenge decisions to confine them there.

"The prisoners here aren't looking to get rich. They are looking to get conditions improved there," Sternstein said.

Normally, the nearly 600 inmates in the Lorton Youth Center's two compounds live in dormitory settings where they have their own rooms that they can lock, Ridley said. Most of the inmates are between 18 and 22 years old. Because of their age they have been sentenced by the courts to serve indeterminate prison terms under the liberal provisions of the federal Youth Corrections Act.

The 26-cell Adjustment Unit, a one-story, brick building in a far corner of one of the prison compounds, houses what Ridley calls the "behavioral problems" from among the general population at the prison. Some inmates who are in protective custody, either because they requested it or because it was ordered by the court for safety reasons, are also held there.

Two classes of prison-rule offenders are held in the Adjustment Unit, Ridley said. One group can be held a maximum of 14 days for minor violations, such as for being "disrespectful and threatening" to a correctional officer, being in an unauthorized area or possession of food from the culinary unit.

Serious violators, such as those who assault the prison staff or carry weapons, can be held 30 days or longer, Ridley said. He claimed that an Adjustment Unit committee makes recommendations to him about release, but attorneys for the inmates claim that testimony in behalf of the prisoner who faces the punishment is limited unfairly.

Some inmates have stayed in the unit as long as 11 months, depending on their adjustment and offense, and some are held there while under "investigation" for offenses, Ridley said. But inmates allege in the suit that some of them have been held in the unit long after charges against them are dropped and that others are there simply because there is no room for them elsewhere.

Because of the logistics of trying to keep warring inmates segregated from one another, recreation is limited, Ridley said. At present, there are outstanding orders to keep 17 of the inmates held there separated from certain other Adjustment Unit inmates, Ridley said.

Although the inmates lawyers allege that "physical violence" is commonplace in the unit, Ridley said that other than routine fisticuffs, there was only one assault in the last year.

The youth center is one of several sections of the huge prison complex, and its inmates are kept separate from the adult prison population, which is housed in maximum, medium or prerelease facilities.

It was inmates of the maximum security section who won $400,000 and the promise of more guards last year after charging in a fedearl suit that the District government had failed to provide them with adequate security.