Democratic nominee Eleanor Holmes Norton holds a sizable lead in the race for D.C. delegate to Congress, but much of her support is fragile and a large number of voters remain undecided, apparently reflecting the controversy over her income taxes.

Interviews in recent days with 200 self-described likely voters found that about a third have not made up their minds about the delegate race, an unusually large number for the final days of a campaign. Of those who have decided, only one in three is enthusiastic in support of either Norton or Republican Harry M. Singleton, her chief opponent.

Although the interviews were too few to estimate levels of support, they suggest that the failure of Norton and her husband to file D.C. income tax returns for the last eight years deeply troubles many Democrats, who outnumber Republicans by a 9 to 1 ratio in the District.

"It puts a lot of suspicion, doubt, in my mind," said David Titus, 40, a Ward 3 resident who said he leans toward Norton, but only because she is the Democratic nominee. "I don't care who you are, the president or the poor guy digging ditches, you've got to pay your taxes like every other schmo."

Vincent Fields, 33, a Metro bus driver who lives in Ward 5, said he could not make up his mind, even though he almost always votes Democratic. The Norton tax issue, he said, "is one of the key factors I'm undecided {about} . . . . I don't believe her. I'm not mad about it. I just don't believe her."

Such concerns appear to be greatest among whites. Although Norton apparently enjoys a substantial lead among the blacks interviewed, she is at best breaking even among whites. Further, more than half of those interviewed who are still undecided are white, though white voters make up only about a third of the electorate.

But the interviews also suggest that even those who are backing Singleton do not know his record and are doing so in large part as a protest against Norton.

The 200 voters were questioned before The Washington Post endorsed Singleton, a former Reagan administration official who now operates his own consulting firm. Alvin Thornton, a political science professor at Howard University, said yesterday The Post's endorsement on Wednesday "could cut both ways," legitimizing a largely unknown candidate but also increasing sympathy for Norton among residents who dislike the newspaper's coverage of the community.

Thornton added that the results of the interviews showed that "absent Mrs. Norton's tax problems, the race would be over completely."

Norton, who headed the Equal Employment Opportunity Commission in the Carter administration and is now a Georgetown University law professor, has said her husband, Edward, handled their finances and that she did not know he had failed to file their tax returns for tax years 1982 through 1989.

In the interviews, many residents said they could not believe someone would be so unaware of something as basic as filing income taxes.

"The woman purports to be a legal scholar and professor, and to pull the old dumb blonde routine is beyond the pale," said Gabrielle Hill, 50, an educator who lives in Ward 6. "She's been futzing and fuddling on this for enough weeks and has had a number of chances to turn it around and it's gotten worse. Every time I read about it, it gets worse."

Hill said she would vote for Singleton, though "I'm not that comfortable with my knowledge about his background."

"Somewhat reluctantly, I'm supporting Singleton," said Josephine Dudley, 79, a Ward 3 resident. "I would have normally voted for Norton until she got into all this tax mess. I think anybody ought to take care of their affairs a little better than that. I think she tried to get out of it and cover it over and hasn't come completely clean yet. Maybe if she did, I'd think about it, but it's probably too late."

Norton's campaign manager, Donna Brazile, said yesterday that her own sampling shows Norton with "a nice, huge lead." She characterized that support as "very hard," but acknowledged that about a third of all voters remain undecided, in large part because of the tax issue.

Singleton campaign officials declined to comment about the interviews.

Brazile said that Norton would garner a large share of the undecided voters because "people have a tendency to look at someone's record and in the case of Ms. Norton, she has a wonderful record of achievement in the field of civil rights."

Charles A. Harris, 44, a Metro employee who lives in Ward 5, said Norton had "an outstanding record" at the EEOC, adding that she has been "unfairly chastised as far as her tax situation is concerned."

"Her association with the Carter administration has enhanced her as far as I'm concerned," Harris said. "She's a very compassionate individual, someone who's going to be dedicated to the situation and the perils of the city."

Harris said he does not handle the finances in his household and therefore could understand how Norton might not have known about her own taxes. "If somebody comes up to me and asks about finances, I can stand there and look pretty stupid, because I don't know what goes on," Harris said.

Shirlette Miller, 22, a strong Norton supporter who lives in Ward 4, said the tax issue "shouldn't have even been brought up."

"That's between her and her husband, not between her and all of Washington," Miller said. "What does that have to do with her running or what kind of delegate she'll be?"

Likewise, Carolyn Smith, 53, another Norton supporter in Ward 4, praised the candidate as a "fighter for civil rights" and said she knew nothing about Singleton. As for whether Norton knew she had not filed taxes, Smith said, "If she had known, she would have cleared it up before she ran. They {the media} are always looking into things when you're in the limelight."

For BeLinda Jackson, 25, also a Norton supporter from Ward 4, too much emphasis has been placed on taxes -- a complaint echoed by others.

"I'd like more information on them, besides what they did bad," she said. "I pay the tax issue some mind. I'd like to know where the money went. But I'm really interested in other things. They haven't been talking about housing for the homeless; housing for low income people; or the crime rate, which is just terrible. This other stuff is just distracting."

Taxes, however, will be at the heart of Richard Karlin's decision.

"I don't know what I'll do for sure," said Karlin, 27, a Ward 3 resident. "I know only a little about Singleton. But I know I could not vote for Norton."

Nicole Matthews, 18, a student from Ward 4 who will be voting in her first election Tuesday, said that when she heard about the tax problem, "I said, 'Uh-uh, I'm voting for {Singleton}.' "

"I liked {Norton's} record on civil rights," Matthews said, "but she really should have known better. Everyone needs to take on the responsibility of paying taxes."