The chairman of a House District subcommittee said yesterday that if action is not taken soon to relieve "horrendous overcrowding" at the D.C. Jail, the implications "could be tragic."

Rep. Mervyn M. Dymally (D-Calif.), who heads a subcommittee on judiciary and education, made the comments at a hearing to review overcrowding in the D.C. corrections system and to discuss sentencing alternatives.

The hearing was the latest in a series of recent congressional reviews of overcrowding at local prisons. Sen. Arlen Specter (R-Pa.), who recently toured Lorton Reformatory and the D.C. Jail, has expressed his concern over overcrowding at the jail and a lack of rehabilitation programs at Lorton.

In addition, a U.S. District Court judge said two weeks ago that he may hold Mayor Marion Barry and other city officials in contempt for not alleviating overcrowding at the jail, where more than 2,400 are housed two in a cell in a facility built to hold 1,355 inmates.

Dymally said yesterday that 340 D.C. Jail inmates are housed in bunks outside the cells in recreation and day rooms. "For security reasons, such accommodations have become an unmanageable nightmare . . . creating the haunting possibility of a local Attica or New Mexico-like prison outbreak."

D.C. Corrections Director James F. Palmer said the situation "is being treated with maximum urgency by city officials" and that steps were being taken to move about 900 inmates from the jail to refurbished facilities at Lorton in the near future.

Palmer said overcrowding at the jail also would be reduced "in due course" through increased use of halfway houses.

U.S. Attorney Stanley S. Harris, in response to questions from Del. Walter E. Fauntroy (D-D.C.) on alternatives to incarceration, said the city had a "lenient sentencing system," where probation is "invariably" meted out to first and even second offenders.

Harris said one "critical factor" underlying the problem of overcrowding is that "we have an awful lot of crime in this city," Harris said. "What we have is a system that does not have the capacity to deal with that."

Harris said most of those now incarcerated are repeat offenders and "most of them are violent offenders."

But Francis D. Carter, director of the Public Defender Service, argued that part of the overcrowding could be alleviated by an extensive diversion program where persons accused of nonviolent crimes could be "jettisoned" from the system and given the option of paying restitution, fines or performing community services, rather than being incarcerated.

ACLU prison project director Alvin J. Bronstein urged that consideration be given to setting up work-release centers, such as those in Alabama, where inmates earn wages, pay taxes and pay for part of their housing.