D.C. delegate candidate Eleanor Holmes Norton, seeking to quell the furor about her unfiled city taxes, plans to pay the District an additional sum of more than $5,000 to cover interest and penalties she owes on local income taxes for the past seven years, according to a key Norton adviser.

Norton's planned payment of interest and penalties raises the possibility that she, together with her husband, Edward, owe the city more in taxes than was withheld from their paychecks during those seven years. But it remained unclear yesterday precisely how much the Nortons owed and paid in each of the past seven years and how much of the planned payment reflects a still-outstanding tax liability.

The Norton adviser, who asked not to be identified by name, said yesterday that the interest and penalties for the seven-year period total at least $5,000 and are perhaps closer to $10,000. The adviser also noted that Norton has not filed taxes for 1989, when her income totalled more than $325,000, meaning that yet another payment to the D.C. treasury could be required.

Any new penalty payment by Norton would follow her two tax payments of Sept. 8, when she wrote checks to the city treasury totaling more than $28,500 to cover taxes due for 1982 as well as some interest and other penalties.

Norton, who won the Democratic Party's delegate nomination last Tuesday, plans to disclose the newest interest and penalty payment tomorrow, when she has tentatively scheduled a news conference to try to answer lingering questions about her failure to file city income tax returns for the years 1983 through 1989, according to one of her campaign strategists.

Failure to file D.C. income taxes is a misdemeanor; if willful, it is subject to a fine of $5,000 and imprisonment of up to a year. If not willful, penalties are lighter. After the Nortons' tax problems were disclosed, officials at the Department of Finance and Revenue, the city's tax collection agency, said they were investigating the case. Department spokeswoman Linda Grant declined to comment yesterday on any aspect of the Norton case.

When the tax controversy first erupted, Eleanor Norton said that her accountant believed the amount withheld from her salary and paid in D.C. taxes was sufficient to cover her overall tax liability; she also contended at one point that early calculations showed she was owed a refund by the District government.

Donna Brazile, Norton's campaign manager, declined to discuss any of Norton's tax-related payments to the city, saying that "at Ms. Norton's request, the accountants have been reviewing all of their financial matters."

"A report is in preparation and will be issued shortly," Brazile added.

Meanwhile, Norton's chief opponent in the Nov. 6 general election, Republican nominee Harry M. Singleton, sharpened his recent attacks against Norton, demanding that she reveal the "full extent" of her tax problems and reiterating his contention that her failure to file tax returns for a seven-year period had raised potentially crippling questions about Norton's integrity.

"She refused to pay her taxes year after year, with an apparent arrogance that she was somehow better than the rest of us working stiffs," said Singleton, a lobbyist and former Reagan administration official.

"How could she get away with placing herself above the law?" Singleton added. "How anyone can get away with that, without some civil or criminal liability attached to that, is hard for me to imagine."

Singleton said Norton "ought to suffer the same penalties that anyone else does who fails to file and pay their income taxes."

"There are people losing their businesses in this city, there are people being subjected to tax liens and so forth and prosecutions who haven't paid their taxes. Why is Eleanor Holmes Norton any different from those people?"

In the days since someone anonymously used a facsimile machine to send copies of the Nortons' delinquent tax notice to the media, Eleanor Norton has offered a number of explanations about her and her husband's failure to file city tax returns. She said her husband handled the family finances and that she was unaware of his failure to file, and also blamed the controversy on his "procrastination" to resolve a longstanding tax dispute with the city.

At the same time, Norton has accepted responsibility for what she described as a lapse on her husband's part. In last week's Democratic primary election, the disclosure about the Norton taxes cut deeply into her support in several portions of the District, though ultimately Norton won the five-way contest decisively.

The adviser also said that because of the interest, penalties and other adjustments to their local tax returns, the Nortons also must now make adjustments to their federal returns for each of the seven years. It was not immediately clear whether the U.S. government is owed any money because of those adjustments.

Singleton, in response to a reporter's question, said his local and federal tax payments had always been in order. "As far as I know they are," Singleton said. "I file my taxes. I paid my taxes, both local and federal."