Attorneys for inmates at the D.C. Jail asked a federal court judge here yesterday to find Mayor Marion Barry in civil contempt and fine him $50,000 for violating the court-ordered inmate population ceiling at the facility on Dec. 7 and for the subsequent attempt to cover it up.

They also asked that a $5,000 fine be imposed for any subsequent violation of the Aug. 22 court order that limited the number of inmates at the jail to 1,694.

"No institutional reform can be expected without the moral condemnation of a finding of contempt, an official declaration that the court will not condone disregard of its orders and will be especially severe when the attempt is made to conceal the violation," the attorneys said in papers filed late yesterday.

The inmates' request came five days after lawyers for the District government admitted that some D.C. Corrections Department officials and employes had engaged in a "deliberate effort to conceal the truth" about the violation from the court and from Director of Corrections James Palmer.

In other action on the District's prison problems, members of Northern Virginia's congressional delegation and the chairman of the Fairfax Board of Supervisors met with Justice Department officials to discuss the problems' effect on Lorton Reformatory -- the city's prison in Fairfax County -- sections of which are also under court orders to reduce overcrowding.

Sens. John Warner and Paul S. Trible, Rep. Stan Parris and Chairman John F. Herrity had hoped to persuade Deputy Attorney General D. Lowell Jensen to reinstate an arrangement, canceled by the federal government last week, under which newly sentenced city inmates were sent to federal prisons.

They said later that the Justice officials said they might reconsider the agreement if the District moves quickly to select sites for temporary facilities and a permanent prison in the city. Congress has allocated $30 million for a new prison.

Federal officials had no comment after the meeting.

Also yesterday, a commission appointed by Barry and the D.C. City Council to investigate building a new prison in the District announced that they had voted 9 to 6 against new construction, favoring instead alternatives to incarceration.

In requesting the imposition of fines, attorneys for the jail inmates noted that the city had previously violated court agreements on jail overcrowding and told the court that "the likelihood of future violations, and the temptation to conceal them, will endure and grow stronger."

"It is painfully clear that even the drastic remedy of contempt is not totally effective to motivate these defendants to perform their duties," the request stated. It also pointed out that the reason the federal government will no longer accept newly sentenced inmates was "because of city officials' failure to live up to their commitments."

The inmate population at the jail reached 1,742 on Dec. 7 when some scheduled transfers did not take place before the official 4 a.m. count.

According to testimony at two hearings about the Dec. 7 incident, Corrections Department officials attempted to change the official count to show falsely that the jail was in compliance and later denied that a violation had occurred.

Under the plan proposed by the inmates' attorneys, the $50,000 fine would not have to be paid for 180 days and would be rescinded if the city stayed in compliance for the entire period.

The city has five days to file a reply to the proposal.