Mayor Marion Barry and the District's senior tax collection official said yesterday that Eleanor Holmes Norton and her husband received no political favoritism in the seven years they failed to file local income taxes.

Barry defended the city's tax enforcement program, describing it as "almost 99 percent" effective in detecting delinquent taxpayers.

Harold L. Thomas, director of the D.C. Department of Finance and Revenue, the city's chief tax collection agency, said it is relatively easy for taxpayers to secure from the District government a complete record of their individual tax histories, including notices of any unpaid taxes.

An official in Norton's campaign for D.C. delegate, which was hit last month by the disclosure of the Nortons' tax problems, said yesterday that the candidate has requested but not received copies of all records pertaining to the Norton family's D.C. tax history.

The campaign official, who asked not to be identified, said Norton was granted access to some of the records while reconstructing her tax history, which led to her paying the District nearly $89,000 in back taxes and penalties. But, the official said, "neither Eleanor nor her accountant has in their hand the physical file of her records."

Norton has refused to release copies of her joint local or federal tax returns, saying her husband believes it would violate his privacy.

Barry and Thomas, who with other city officials met yesterday with reporters and editors of The Washington Post, said city law prohibits them from discussing the details of the Norton tax case. But the mayor and Thomas suggested strongly that the Nortons would have been alerted to their tax delinquencies, and stated firmly that the couple received no preferential treatment after failing to file.

Eleanor Norton, a Georgetown University law professor, held a high-ranking position in the Carter administration and is noted for her work in the civil rights movement. Her husband, Edward, is a lawyer and served as chairman of the D.C. Board of Elections and Ethics during part of the time the couple failed to file their local taxes.

Barry said "it is very difficult" for delinquent taxpayers to go undetected for several years, and Thomas echoed that view: "It is most unlikely that a person who is or who should be paying taxes and who is working and residing in the District can go undetected ad infinitum."

Barry added that the city can detect recalcitrant taxpayers "almost 99 percent of the time," and that once a taxpayer is found to be delinquent, "something does happen to you." Enforcement powers include sending notices, filing liens against property or seizing assets, he said.

Thomas noted that the enforcement system is not foolproof. "In any major system that monitors or regulates anything, there are instances or items or individuals that may go undetected for one reason or another," he said.

Thomas added that neither the Nortons nor any other taxpayer has received preferential treatment after not filing their taxes.

"I can assure you no taxpayer that's come to my attention for any reason has gotten any favorable treatment," Thomas said. "We treat all taxpayers similarly and we try to treat them equitably . . . . We do not grant exceptions to any taxpayer based on favoritism."

Thomas said his department is willing to send taxpayers copies of their individual tax histories, and frequently shares copies of such records with delinquent taxpayers to encourage them to pay back taxes.

Norton was endorsed yesterday by the Sierra Club, and met for 40 minutes with House Speaker Thomas S. Foley (Wash.) and other House Democratic leaders.

Norton said last night that during her meeting with House leaders, she raised the issue of her D.C. tax returns, repeating her position that she did not know her husband had failed to file them.

Foley "was very sympathetic to me," Norton said, telling her that his wife does their taxes and "he would not know a thing about them." She said that Foley also told her "people here are going to consider it an honor to serve with you."

Staff writer Steve Twomey contributed to this report.