The Greater Washington Board of Trade yesterday threw its weight behind the campaign to defeat the D.C. educational tax credit initiative, urging its members to "provide both financial and active support" to efforts to defeat the measure.

The board, the largest organization representing the city's business community, rarely takes public stands on ballot questions. But Flaxie Pinkett, a Realtor and chairman of the board's legislative bureau, told a news conference yesterday that the organization's executive board unanimously voted to oppose the initiative because it felt the measure would drain the city treasury of at least $24 million, lead to an increase in business and property taxes and result in "the degradation of educational quality."

Despite the board's strong words against the initiative, it will not directly give money to one of the groups actively fighting the measure since its by-laws prohibit such contributions, said J. Pat Galloway, the board's president. Galloway also said that while the board has asked its members to make voluntary contributions, it had not set any quotas and he has no idea how much money would be raised from board members.

While opponents of the tax credit hailed the board's action as a significiant boost to their campaign, supporters of the initiative dismissed it as unimportant.

"I can't see them swaying people one way or another," said Jule Herbert of the D.C. Committee for Improved Education, a local offshoot of the National Taxpayers Union and the main group supporting the initiative. "I never heard anyone say they were going to vote for something because of what the Board of Trade says."

Under the tax credit proposal, taxpayers would be able to reduce their D.C. income taxes by up to $1,200 per pupil for expenses they incur at either private or public schools. It would also permit nonparents and corporations to contribute their tax credits toward educating low-income youngsters.

Although the initiative would provide tax advantages to businesses making donations in behalf of students, Pinkett said the board nevertheless decided to oppose the measure.

She said board leaders "felt this financial advantage to businesses was unimportant in view of the harm that the initiative itself would bring to the entire community.

"We are more concerned with the welfare of the community and its public education . . . than we are in a small financial benefit to our corporations and businesses," Pinkett said.

The tax credit plan was attacked on two other fronts later yesterday, once at a heated public hearing in a predominantly black, middle-class area of Northwest Washington and again at a gathering of educators addressed by Albert Shanker, president of the American Federation of Teachers.

About 65 4th Ward residents, fearful that the credit would force the city to raise property taxes and reduce spending for public schools, jeered two proponents of the measure at an advisory neighborhood commission meeting held at the 4th District police station. City Council Chairman Arrington Dixon attended the meeting to voice his opposition to the proposal.

Many of the residents who spoke said they viewed the proposed credit as an attack on the public school system that was launched by outsiders who had no vested interest in the future of the city.

"I don't see how this would help the D.C. public schools," said Fred Dendy, a federal government printer who has a daughter at McKinley High school. "I think it would hurt more than it would help."

Ishmael C. Kelley, of 6625 Piney Branch Rd. NW., who has two children in private schools, said he was "bitterly opposed" to the credit, adding that "I'm willing strongly to pay my own damn tuition."

Alice Biles, a retired D.C. school teacher, said she viewed the credit proposal as an unfounded attack on the public schools. "Many successful people today are products of the public school system," she said.

Alvis Adair, an educator and candidate for delegate to the statehood constitutional convention, contended that proponents of the credit had little regard for the Washington school system because the overwhelming majority of the students are black.

"Is this a new form of racism developing?" he asked.

Manuel Dunbar and Robert S. Marlowe, the two spokesmen for the D.C. Committee for Improved Education, argued that the credit would increase educational opportunities for residents and improve the quality of education by forcing public schools to compete with private schools.

Meanwhile, at a conference on tuition tax credits sponsored by the National Institute of Education, Shanker blasted the D.C proposal as a "fiscally irresponsible measure" that threatens the long-term survival of the city's school system.

Shanker said the tax credit proposed in Washington was the largest and most radical offered anywhere in the country, and predicted that if adopted, it would strip the citys schools of "all the kids except those who private schools won't accept."