The local chapter of the American Civil Liberties Union and a number of other politically active groups yesterday announced opposition to a mandatory prison sentencing measure being proposed as a citizens initiative for the Sept. 14 ballot.

"It is . . . little more than a politically expedient measure that will in the long run impede true reform of the criminal justice system," said Leslie Harris, executive director of the National Capital Area ACLU. Harris said the measure creates "an illusion of law reform."

The mandatory sentencing bill, proposed in early March by City Council member John Ray (D-At Large), a candidate for mayor, would impose minimum sentences of five years without parole for first offenders who use a firearm to commit a violent crime, and 10 years for a second conviction.

The bill also would require persons convicted of selling illegal drugs to serve up to four years in prison without parole, depending on the drug.

Harris, who released a 70-page ACLU study opposing mandatory sentencing, said the measure would "not reduce crime" but instead would increase the city's cost of housing prisoners at Lorton Reformatory and the D.C. Jail. She said the city would be better off spending the money on education, job training and crime prevention rather than prisons.

In addition to the ACLU, other groups that announced opposition to the measure included the Washington Urban League, the Gray Panthers, the NAACP's local chapter, the Gertrude Stein Democratic Club, the National Black Lawyers, the social services office of the Catholic Archdiocese, Local 1550 of the American Federation of Government Employees, the Gay Activist Alliance, and the National Moratorium on Prison Construction.

Ray and a group called the Citizens for Safer Streets Committee have turned over to the D.C. Board of Elections and Ethics more than 22,000 signatures--about 8,000 more than needed--in an effort to get the bill on the ballot.

The board is expected to rule April 7 whether the measure meets the city's legal requirements and begin certifying the signatures.