In late June, as the final days of its budget year fell away, Prince George's County signed its largest-ever contract with a minority firm, a five-year agreement that could be worth $17.6 million to Maxima Computer Systems Corp. of Rockville.

That milestone, however, still left the county far short of its goal to do 30 percent of its business with minority companies -- and far from satisfying increased demands that blacks get a piece of the county's growing economic pie.

"The system is not set up to ensure that minorities can participate," said County Council Chairwoman Hilda Pemberton. "We have to change that."

Beginning today, when the County Council returns from its recess, the subject will be more than goals to deal with the complaints of black business leaders and elected officials.

Momentum is building for a set of specific, mandatory guidelines to guarantee that minority firms in the nearly half-black county get their share of the millions of dollars spent in county and agency contracts.

The push for stronger measures in public contracting reflects the black community's growing voice in political and economic matters in Prince George's, a voice given resonance by census figures showing the county has among the best educated and most affluent blacks in the country.

An average black family in the county has an income of nearly $23,000, compared with $12,600 for blacks nationwide. Moreover, the county ranks sixth in the nation in numbers of black-owned businesses, with 5,762.

The economic renaissance that has washed over the county in recent years only adds urgency to the demands of minority leaders that minorities get preference in bidding for county-purchased goods and services.

Like their counterparts in the District and Baltimore, blacks in Prince George's are demanding a greater share of the action and are increasingly willing to nudge political leaders such as County Executive Parris Glendening to help blacks achieve that goal. Such urgings play to Glendening's good side, since the promotion of economic development has been his political forte, and the county executive is expected to come up with his own proposal this fall.

In the views of black elected officials, business leaders and the heads of the NAACP, the Black Democratic Council and other organizations, economic matters will be the paramount issue in the black community through the 1990 county elections.

For two years, the county has set a goal of doing 30 percent of its business with minority firms. Yet, despite the major contract awarded in June, the figure for the last budget year was closer to 20 percent. In dollar terms, however, the amount was nearly double that of two years earlier.

The issue came to a head in July when a coalition of black groups delayed a Glendening appointment to the Washington Suburban Sanitary Commission, a utility authority that provides water and sewer service for Prince George's and Montgomery counties. The coalition had voiced concerns that the authority had not awarded a fair share of contracts to minorities, a charge that commission officials dispute.

Glendening, who has been strongly allied with minorities, angrily accused the black groups of divisiveness. And when Pemberton arranged a private meeting between the nominee and black critics to work out concerns, Glendening assailed her for holding closed meetings, which he said played into the hands of those trying to racially divide the county.

Black political leaders said they would continue to oppose political appointees to agencies that failed to meet contracting goals and would work to strengthen affirmative action hiring for county government.

"I don't particularly care for a confrontational posture, but sharing the power is sharing the wealth," said John Spearmon, a spokesman for the Coalition for Black Economic Development, which represents the NAACP, the National Business League and the Black Democratic Council.

So far, three proposals to remake the county's minority contracting program have emerged.

In meetings with Glendening in the spring, black county and state elected officials pushed for stronger measures, including a set-aside program under which bidding on a minimum of 30 percent of procurement contracts would be reserved for minority companies. Glendening, who plans to unveil his program this month, has resisted a so-called sheltered market program, but he has said he would consider set-aside provisions so long as there are safeguards against abuse.

Under Pemberton's plan, meeting minority contract award goals would be tied into the job evaluations of department supervisors. Procurement officers would have a number of tools available to them, including set-aside bidding for minority companies and a modified system of awarding bonus bid points based on the level of minority participation.

The Coalition for Black Economic Development, which delayed the sanitary commission nomination, will propose legislation that calls for a minimum of 37 percent of contracts to go to minorities.

"I'm afraid that if we are not careful, blacks on a whole will once again miss an economic window. There is enough history to look back and see that good faith in many instances does not do what is necessary," Spearmon said.