The National Taxpayers Union has given another $10,000 to the effort to win approval for an educational tax credit in the nation's capital, continuing its role as the measure's chief financier, according to records filed yesterday with the D.C. Office of Campaign Finance.

The latest NTU contribution brings the group's total contribution to the campaign to $124,091, or about 99 percent of the $125,429 raised by the D.C. Committee for Improved Education, the local organization spearheading the drive for the $1,200 per pupil tax credit.

The NTU's continued financing of the tax credit campaign yesterday renewed charges by opponents of the measure that the tax credit campaign is part of an overall conservative strategy "to destroy government in the District of Columbia."

"The NTU doesn't care if anybody in this city gets an education," said William H. Simons, president of the Washington Teachers Union. "They are just using this as a vehicle in their overall strategy to destroy government.

"Very little attention has been given to the true objective of these radical right groups because they use quote -- legal -- unquote means," Simons added, pointing to the group's sponsorship of tax limitation campaigns elsewhere, such as the one known as Proposition 2 1/2 in Massachusetts.

James Dale Davidson, the 34-year-old founder and chairman of the Taxpayers Union, said yesterday that the attacks on the NTU's financial contributions were "complete rubbish" and "insincere." Those contributions are no different from the money national labor unions, such as the American Federation of Teachers, have given to groups opposing tax credits, he said.

"There's no equivalent objection when labor unions spend their money," said Davidson.

Meanwhile, three groups opposing the tax credit initiative estimated yesterday that they would spend a total of about $75,000 in their campaign, with the bulk of that apparently coming from labor unions such as the AFT.

Precise figures were unavailable, however, because the two-week-old Coalition Against Tuition Tax Credits, a group of unions and civic organizations, missed a Monday deadline for filing its first financial report with the finance office.

Davidson described the National Taxpayers Union as a "moderate organization which is trying to do exactly what we claim we're doing, and that is representing the unrepresented interests of ordinary people." He described the union's attempts to portray his group as an arm of the right wing as "asinine."

Attempts to discredit NTU have been a central part of the campaign against the tax credit initiative. The American Federation of Teachers, for example, has printed up leaflets entitled "The Truth About NTU" that labels the group a "right-wing organization" that advocates a variety of "bizarre positions."

The 10-year old organization, which has a dues-paying membership of about 120,000 and an annual budget of $1.8 million, has conducted scores of anti-government-spending campaigns that cut across ideological lines. Davidson said it has joined liberals in fighting the B1 bomber, while lining up with conservatives to sponsor a "balance the budget" constitutional amendment in state legislatures.

Its board members over the years have spanned the political spectrum, Davidson said, ranging from linguist Noam Chomsky to economist Murray Rothbard. Others who have, at one time or another, been affiliated with the group include Washington Monthly editor Charles Peters, Maryland State Senate president James Clark and Ernest Fitzgerald, former Pentagon official who blew the whistle on the cost overruns of the C5A cargo plane.

Davidson said his group decided to become involved in the tax credit campaign because the District was an excellent example of a city that has suffered from migration caused by "atrocious" public schools. He contended that a tax credit for public or private schools would help middle-class blacks who are now deprived of educational choice.

Nevertheless, tax credit proponents, sensitive to criticism that they have been funded by an outside group, launched a counteroffensive this week by accusing the opposition of improperly using city manpower and resources to try and defeat the measure.

Kent Guida, a spokesman for the Committee for Improved Education, noted that Mayor Marion Barry has said he will "mobilize the D.C. government" to defeat the initiative, including instructing city employes to pass out information sheets attacking the proposal.

"We don't want to see taxpayer money used to try to defeat an initiative," Guida said.