When the Greater Washington Research Center issued a report this week calling into question the future financial stability of Fairfax County, the county's board chairman was so angry he challenged Robert McNamara, the director of the report's task force, to a debate.

The reaction to the six to 10 yearly products issued by this tiny think tank usually isn't that sharp. The center normally operates in relative obscurity, making news for a day or two after its latest study is issued.

But in its five years of existence, the center has emerged as an influential, neutral voice on public policy issues. Its efforts to accurately define issues in the Washington community and to scrutinize the costs of services to local governments have done more than help its business members plan the best location for a new shoe store or bank branch.

"It's raised citizen awareness of crucial public issues, such as the cost of Metro," said Walter Scheiber, director of the Metropolitan Washington Council of Governments.

Any dispute that arises is welcome, said the center's executive vice-president, Atlee Shidler. "It's our business to stimulate thought and controversy," he said. "We thrive on it."

Created in 1978 when the four-year-old D.C. Municipal Research Bureau was merged with the Washington Center for Metropolitan Studies, the center is supposed to provide independent, nonacademic research on the Washington area.

Unlike many centers studying regional problems, it is not affiliated with a chamber of commerce or any government. A private group, two-thirds of its money comes from its 140 members, mostly local retailers, law firms, banks and the like, who pay between $250 and $10,000 a year to belong.

The remaining support for the center's $340,000 annual budget is provided by foundations, chiefly the Eugene and Agnes Meyer and Ford foundations.

Housed in several rooms of an office building on Massachussetts Avenue, two doors down from the sprawling Brookings Institution, the center has only six employes. Directing the project are Shidler, who has been studying Washington since he helped Pulitzer Prize winner Constance M. Green research her history of D.C. in 1957, and Philip Dearborn, a respected former financial counselor to the D.C. mayor, the city of Cleveland, Fairfax and the federal Office of Management and Budget.

Special reports, like this week's report on municipal finances, are authored either by the staff in conjunction with a volunteer group of experts or by experts hired on a project-by-project basis.

Robert McNamara, for example, retired president of the World Bank and former boss of the Ford Motor Company and the Pentagon, was chosen to direct the task force "because of his enormous experience with data and information and analysis," said Shidler. "He wondered whether the fact that he really didn't know the local life of the Washington area would be a handicap. But he loved this town and seemed to want to make a contribution to civic betterment, an old-fashioned term, toward Washington."

McNamara "participated intensively" in the report, conducting all 20 of the task force's meetings over the last year, Shidler said.

Other experts who often work for the center are George and Eunice Grier, local demographers responsible for "Trends Alert," the center's exhaustive study of the 1970 federal census data for the region, and "Baby Bust," the pioneering 1971 study that found the nation's birthrate was dropping.

The center works closely with, and has been confused with, other civic groups such as COG, or the Board of Trade, or the Federal City Council, a group of 125 business leaders.

It counts among its successes the formation of the Cultural Alliance of Washington, which brought together dozens of arts groups, and the theory that the area is expanding in several centers, rather than growth moving evenly outwards.

The center has published studies on the cost of Metrorail to local governments, the movement of blacks to the suburbs and welfare trends in the Washington area.

In the main, local governments and businesses say the center provides sophisticated research, particularly on what type of people live where, and that helps them plan services. But the center hasn't lessened governments' dependence on their own research departments, and some government officials say the center's studies duplicate their own.

"I don't read all their reports," said Elijah Rogers, D.C. city administrator. "We have a planning office that does that work for us anyway. I respect the people there, but I think some of it is duplicative."

But reaction to the center's work rarely is as explosive as that of Fairfax Board Chairman John F. Herrity, who called their study of local finances "full of baloney" and "dishonest."

Dearborn, who authored the report, is unperturbed by the fuss: "You want people to react to it. We want Fairfax to develop their own projections and keep pushing ahead on understanding their finances. This isn't unique. In the District, this mayor and his predecessor have both had harsh words for us. But when they're not mad at us, then they would say we're honest and thorough.

"Our only role is that of a gadfly."