A U.S. District Court jury yesterday found that the District of Columbia government has failed to provide adequate safety within the maximum-security-facility at Lorton Reformatory, and awarded about $600,000 in damages to 400 inmates.

In what lawyers described as the first court decision of its kind, the jurty determined that the city had violated the inmates' constitutional right to be free from cruel and unusual punishment while in prison.

Specifically, the jury awarded $1 for each day of imprisonment to each inmate held at the maximum-security facility from July 4, 1976, until yesterday. Attorneys for the inmates estimated yesterday that the verdict means that each inmate could receive as much as $1,500.

About 400 inmates were included in the class-action lawsuit first brought to court by a group of jailhouse lawyers. The case was heard during an eight-day trial before Judge June L. Green, and the inmates were represented by attorneys from the Washington law firm of Covington & Burling.

The inmates at the maximum-security facility, which houses most of the city's most dangerous criminals, had contended in a class-action suit that there were not enough guards in their wing of the sprawling complex in suburban Fairfax County.

They said drug and alcohol abuse was widespread, weapons were easy to come by, violence was commonplace and inmates being brought to the facility for the first time were routinely mixed in with hardened, long-time prisoners and those with mental disorders.

Peter J. Nickles, one of the lawyers who represented the inmates, said of the jury's decision. "They found that the conditions at maximum were such as to violate the basic standard of decency required by the Constitution of the United States."

In addition to the constitutional claim, the jury also found that the city had been negligent in its duty to provide safe conditions for the inmates in maximum security.

Now that the jury has resolved the questions of damages, Judge Green must consider the inmates' additional request that the court order the city government to take specific steps to improve security conditions at the maximum facility.

Assistant D.C. Corporation Counsel Leonard Bren, who was present in the courtroom when the jury foreman announced the verdict at 5:20 p.m. yesterday, said the decision could be appealed. But Bren would not say immediately if an appeal would be made.

Corporation Counsel Judith W. Rogers said, "I am disturbed by the facts giving rise to the case, and the results, and I am examining the legal issues to determine the nature of further appropriate action."

Rogers said that Mayor Marion Barry was "concerned about the extent to which he may be forced to spend money the city doesn't have, a court suit notwithstanding. [But] he is committed to meaningful rehabilitation of Lorton residents and to humane and decent treatment. He realizes that these are longstanding conditions."

The jury of four men and two women deliberated for more than nine hours over two days before reaching its decision.

By its verdict, Nickles said, the jury rejected the city government's argument that the inmates themselves by their silence about assaults at the facility and by their use of weapons have contributed to unsafe conditions there and thus were not owed any damages.

Attorneys for the inmates also contended that the number of assaults at the institution for the first six months of this year was more than the total number of assaults reported for all of last year. Records on those incidents were turned over to the jury during its deliberations.

Bren, representing the city, told the jury that those assaults amounted to nothing more than major arguments among the inmates or between guards and inmates that did not rise to the level of any constitutional violation of the inmates' rights.

Bren had urged the jury to keep in mind that the maximum security facility is not a "Boy Scout camp" where those kinds of assaults would be the subject of concern.

Nickles, however, described the situation in the maximum security wing as a "war zone" where inmates armed themselves with homemade knives and other weapons because they lived in constant fear of one another.

A group of 16 inmates from Lorton's maximum facility first filed two lawsuits on their own behalf in the D.C. Superior Court in May 1979, protesting conditions at the prison unit. After a judge reviewed the inmates' claim, he appointed the law firm of Covington & Burling to represent the inmates. Last July, the attorneys filed a new lawsuit in federal court, which was decided by the jury yesterday.

The case spawned a series of separate legal actions against the city government two months ago when city officials tried to reduce the number of guards at the maximum security facility as part of its budget cutbacks.

Ultimately, the city government assured both the federal trial and appellate courts that the number of guards at that facility would not be reduced below 122. This week, however, attorneys for the inmates told Judge Green that they have evidence that the number of guards has dropped to 110, which city lawyers dispute.

As a result, Green is scheduled to hold a hearing Monday to determine whether the city government should be held in contempt of court for violating the agreement on the number of guards.

By law, the inmates were allowed to make a claim for damages for a period beginning as early as three years prior to the date when they filed their lawsuit and extending to the date of the jury's judgment.

The exact amount of the award to each inmate will depend on each inmate's term of incarceration. Lawyers for the inmates expect most of the 400 men in maximum security to qualify for full awards of $1,500 each.