The Prince George's County Council agreed yesterday to let voters decide whether county law should be changed to let a part of county business be set aside exclusively for minority contractors.

But even leaders of the drive to increase minorities' share of county business remained cool toward the November 1988 vote, expressing concern that it could yield a divisive campaign or end in a setback for their efforts if defeated at the polls.

A week ago, the council voted to strengthen its voluntary efforts to reach a goal of doing 30 percent of business with minority companies in a county in which minorities account for 46 percent of the population. But the council balked at establishing a mandatory amount of contracts that could be bid on only by minority firms. The District, with 70 percent black residents, has set a goal of awarding 35 percent of its contracts to minorities.

Council Chairman Hilda R. Pemberton pushed for the November referendum vote on changing the county charter after attorneys said that the present law prohibits the council from setting up a mandatory program.

"We heard from a number of people that the only way to get parity is through a set-aside," she said yesterday after the council voted 6 to 3 to submit the question to voters. "This will give {voters} a chance to say that is true. It {the charter amendment} is not a give-away program, it is not costly. I believe it will be passed by voters."

State Sens. Albert R. Wynn (D-Prince George's) and Decatur W. Trotter (D-Prince George's) expressed doubt that the referendum will be passed by voters because it could be seen as a give-away program. If it fails, they said, the set-aside movement could be permanently derailed. "It will be difficult for us to muster the forces for us to win," Trotter said.

The question also enjoys little support -- for a variety of reasons -- among elected officials and black community and business activists.

County Executive Parris Glendening had opposed the referendum, maintaining that the beefed-up voluntary program will allow the county to reach its minority procurement goal.

Members of the Coalition for Black Economic Development, which includes the National Business League of Southern Maryland and the NAACP, contend that a charter change is unnecessary and that a set-aside program is legally permissible under the existing charter. They have said they will test that theory in a lawsuit.

"We have no responsibility for it {the charter amendment campaign}," said Steve Brown, executive director of the county branch of the NAACP. "There is no assurance that this will pass the voters."

The referendum may have had an easier chance if it were on the ballot during the March primary, when blacks voters are expected to turn out in large numbers in support of Democratic presidential candidate Jesse L. Jackson. County law dictates that a referendum must be voted on in a general election.

Pemberton, who sponsored the proposal along with council member Jo Ann T. Bell and Floyd E. Wilson Jr., still maintained that the referendum has a good chance of passing.

But without the active support of the coalition and black elected officials, the twin driving forces behind the push for a set-aside, Pemberton may face a difficult battle. Pemberton proposed the charter amendment as a way to ease council fears that without it the county could open itself up for a lawsuit if a set-aside program was put in place.

It also has been viewed as an attempt to appease the black business community, which insisted that a mandatory program was the only way minority companies would get a share of lucrative county contracts during an unprecedented building boom.

The council's legal advisers have maintained that a set-aside system is prohibited by the county charter, which requires competitive bidding under most circumstances. Even under a set-aside program, the county contracts would only be awarded after competitive bidding among minority-run companies.

Before yesterday's vote, council Vice Chairman James M. Herl and council member Sue V. Mills gave tepid support because they said they needed direction from voters on the set-aside issue. Wilson, who sponsored the mandatory set-aside bill defeated by the council last week, first agreed to support the charter amendment. On Monday, however, he said he felt it was unnecessary, then reversed himself and voted for the measure yesterday.

Council members Anthony Cicoria, Richard J. Castaldi and F. Kirwan Wineland voted against it.

Since the start of fiscal 1988 on July 1, the county has awarded 24 percent of contracts to minority firms, up from 19 percent at the end of the last fiscal year.