A private criminal defense lawyer is seeking to overturn the District's controversial mandatory sentencing law by turning against the city an argument put forward by the government itself in another court battle.

The mandatory sentencing measure, passed in 1982 as a referendum known as Initiative 9, required for the first time that people found guilty here of certain drug offenses or of violent crimes committed with guns receive mandatory minimum prison terms with no chance of parole.

Now, lawyer Brenda Grantland has argued in D.C. Superior Court that the law is invalid because it forces the city to appropriate funds. That, she argues, violates a prohibition set out in a 1981 D.C. Court of Appeals ruling against voter referendums that require appropriations.

The District itself used a similar argument in another Superior Court case -- its effort to overturn the referendum known as Initiative 17, which was approved overwhelmingly by D.C. voters last year that would require the city to provide adequate shelter for the homeless.

In that case, which is currently being reviewed by Superior Court Judge Annice M. Wagner, city officials have argued that the law, if it is allowed to stand, could force the city to spend up to $60 million each year to provide shelter to every homeless person who lives in Washington.

At the time the mandatory sentencing measure went into effect in 1983, corrections officials here estimated that the law would add 250 to 300 inmates to the prison at a cost of more than $15,000 a year each.

This week, Superior Court officials said their records do not show how many persons actually have been sentenced under the measure.

Grantland has subpoenaed a study she believes was conducted by the U.S. attorney's office on the fiscal impact of the sentencing measure. However, a spokesman for the office said yesterday prosecutors will move to block the subpoena. He refused to comment further on the case.

The challenge, set for argument June 28, comes in the case of John A. Green, a 19-year-old D.C. man who pleaded guilty in March to possession with intent to distribute phencyclidine (PCP), according to Grantland, his attorney. Green would receive a mandatory 20-month term because the crime falls under the mandatory sentencing statute.

"Because he has never been in trouble as a juvenile, the judge would have discretion to consider his background and I don't think he would be subject to that harsh a penalty, if it weren't for the mandatory minimum law," said Grantland.

Grantland has argued in court documents that the District's argument in the case involving the homeless referendum "applies with equal force" to the mandatory sentencing law, "since the effects of the initiatives are virtually identical. Both require the governmemt to expend funds for housing, and the expenditure is nondiscretionary . . . . "

In the homeless case, proponents of the measure have argued that following the District's theory would permit political opponents of any initiative to invalidate it "based upon the inevitable fiscal effect of any new legislation."

D.C. officials, however, have asserted that their argument is "more narrow," and is based upon another D.C. Court of Appeals ruling that holds an initiative unlawful if it is an "affirmative effort to appropriate funds."