The Maryland attorney general's office has said that a mandatory set-aside program for minority businesses would be allowable under existing Prince George's County law, thus renewing questions about the need for next year's scheduled referendum on the county charter.

The attorney general's opinion, which is not binding, bolsters the position of black groups that have been pressing county officials to direct some contracts to only minority firms.

The opinion, issued Friday, conflicts with that of County Attorney Larnzell Martin. The county attorney had said that unless the county charter is amended, a set-aside program could be struck down by the courts as being inconsistent with the county's competitive bidding requirement.

Based on Martin's advice, the council voted last month to reject a proposal that would have set aside 30 percent of contracts for bidding by only minority companies. Instead, the council agreed to let voters decide in a referendum next November whether to clear potential legal obstacles to a set-aside program.

Supporters of set-aside legislation said yesterday that the attorney general's opinion appears to support their contention that a charter revision is not necessary. Black business and political organizations, concerned that the county has not met its voluntary 30 percent goal, have pressed county leaders for a stronger program.

Many groups, including the NAACP and the National Business League of Southern Maryland, as well as black elected officials have thrown their support behind a mandatory set-aside program as the only way to achieve equality in contracting. Others, led by council member Hilda R. Pemberton, have supported a more moderate approach to strengthen the voluntary program through a series of incentives.

Council member Floyd E. Wilson Jr., who unsuccessfully pushed for a set-side bill, said the attorney general's opinion did not surprise him.

"We felt all along that there was nothing forbidding it," said Wilson, who plans to reintroduce the legislation when the council returns from holiday recess in January. "There is no need, as I see it, to go ahead with the referendum question."

But County Executive Parris Glendening, after discussions with Martin, insisted again yesterday that a mandatory set-aside program under the existing county charter would not be constitutional.

Pemberton, who has in the past three weeks been working to line up community support for the charter revision vote next fall, said she would make a decision on whether to continue that effort after the county's Office of Law has had an opportunity to review the attorney general's opinion.

Council Chairman Frank P. Casula said he thought it would be safer to allow voters to revise the charter before moving ahead with a mandatory program.

At issue is the county charter's requirement that millions of dollars in government contracts go to the "lowest responsible bidder."

The question, Assistant Attorney General Robert A. Zarnoch wrote, is whether the term "responsible" could apply to the social responsibility of the bidder. The ruling concludes that, based on several recent court decisions, it could.

Also, the ruling said the county's antidiscrimination clause, which prohibits discrimination based on religion, race, color, national origin or sex, could "include the right to bid on county public works and other projects."

"It is possible in some cases for minority business programs and competitive bidding requirements to go hand-in-hand," Zarnoch wrote.