More than a decade after the Negro Chamber of Commerce became the District of Columbia Chamber of Commerce, most business people still regard it as the minority organization, the black equivalent of the Metropolitan Washington Board of Trade.

The D.C. Chamber Board of change that.

The 500-member group is trying to double its membership in the next three months, to broaden its membership base and at the same time increase its clout.

"It's an awesome task," admits executive director James Denson, "but I don't think it is unrealistic."

There are hundreds of medium and small businesses that ought to be D.C. Chamber of Commerce members because of the changing politics of the District and its business community. Denson said.

"Many smallers businesses in the District of Columbia have not belonged to any organization, because they didn't see any reason to."

These firms regarded the Board of Trade as too big for them and the Chamber as too limited in scope.

"In the days before home rule, we couldn't have any impact," Denson explained. With no votes and little money to offer, "lobbying was an exercise in futility" for the Chamber, although not for the more patrician Board of Trade."

"Now you have the rationale and the reason for a lot of companies to join an organization that can represent the entire business community."

The disbanding of downtown progress leaves some gap in the leadership of the business community that the D.C. Chamber can fill. Denson contends.

The city's creation of the new economic development office shows the city government is aware of the interests of the business community.

Although relations between the Board of Trade and the Chamber of Commerce have traditionally been cool - some black businessmen say condescending would be a better term - Denson said that is improving.

The two should be partners, not rivals, contends Denson, who serves on the Board of Trade's steering committees for fiscal and program steering committees. "They address broader issues and we concern ourselves with the District of Columbia," he said.

A certain amount of rivalry is inevitable, not only between the Board of Trade and the D.C. Chamber, but also between the board and the other 14 local chambers of commerce.

The local Chambers of Commerce complain that the Board of Trade siphons off the big businesses that provide the dues and manpower vital for such groups.

Although a majority of its members are minority businesses, the D.C. Chamber in the past year has signed up much of the Washington business establishment. The membership lists now include all three local utility companies, both newspapers ands such big businesses as Woodward and Lothrop. The Hecht Company and Neiman Marcus. The decision of Neiman Marcus to join when it came to Washington last year is helping bring in some other retailers who traditionally limited their activities to the Board of Trade.

Bringing in major firms, Denson said, is vital to the D.C. Chamber's game plan. "Let's face it, those companies employ an awful lot of people and are a very strong part of the tax base of the District of Columbia.

"It increases our clout when we go to the District government. We can say, 'we represent the business community and these are out members.' You have to have this type of membership before you can speak for anything."

Established firms also can help the D.C. Chamber achieve economic independence. It has needed help from the federal Office of Minority Business enterprise because dues haven't been enough to cover operations.

Lawyer Larry C. William Sr. recently was elected to a second term as president of the D.C. Chamber. As Williams and a group of younger, more aggressive leaders flex their muscles, the group will concentrate on specificc issues.

Denson said the District's gross receipts tax on businesses and its real estate tax system - including a proposal to tax business property at higher rates than residential real estate - are major concerns, along with the soaring cost of unemployment compensation.

Also on the adjenda is the commuter tax on which Denson predicts the organization "will take a very long look and a very hard position" on the need for taxing incomes of suburbanites who work in Washington.