THE CHOICE in the race to succeed Walter Fauntroy as D.C. delegate was hard until the last few days. It's much easier now. The next delegate should be Betty Ann Kane. Rival Eleanor Norton's acknowledgment -- she says discovery -- that she and her husband have failed to file D.C. income tax returns for the past seven years is not just disabling, it is disqualifying.

Mrs. Kane is a talented veteran politician who knows city government inside out. Her views are progressive, she has shown a welcome ability to win support from blacks and whites alike, and she would be an articulate, tireless and respected representative of the city's interests in Congress. The office she seeks has been wasted until it all but disappeared from view in recent years. Mrs. Kane has the ability to rebuild it. Her claim in the campaign has been that she has earned the job, has paid her dues by working her way up; but that does her career an injustice. A former school board member, then three-term at-large member of the D.C. Council, she has indeed served the classic apprenticeship. But the point is not merely that she has had her ticket punched. In making the obligatory rounds of the city, attending the hearings, reading the budgets, casting the votes, she has become a genuine expert on the city's rules, means and needs -- and also on its regional and congressional relationships. Mrs. Kane has as well distinguished herself, along with council member John Wilson, as one of the very few on that body willing to wage a continuing struggle against the inefficiencies and worse of the Barry administration. The delegate's office would be in good hands.

Mrs. Kane is not the only worthy candidate in the race; it is an impressive field which any jurisdiction in the country might be pleased to have. Joseph Yeldell, though not our favorite, is a seasoned and savvy municipal and former regional official. Sterling Tucker, former D.C. Council chairman and assistant housing secretary in the Carter administration, served and knows the city well. Donald Temple, lawyer and founder of the promising group Concerned Black Men, is the newest comer in the race, of whom we expect and hope to hear more in the future. But for us the choice came down to Mrs. Norton and Mrs. Kane.

Mrs. Norton's claim to the office had not been an equal familiarity with or history of involvement in city politics or District government. On the contrary, she has had a different career -- a distinguished one -- and had to defend herself against the charge that she would stint District concerns and seek to use the delegate's seat for broader purposes. To us, at least, the promise of her candidacy was that, by virtue of her forceful style and national stature, she would be better able than any other to make the great moral arguments not just for full funding but for full citizenship and voting representation in Congress for the District. It was on that basis that, as of last Friday, we were preparing to endorse her. But it is precisely that rationale -- her superior ability to summon others to support the District -- that her own failure to meet the terms of D.C. law has blown away.

Mrs. Norton says her husband kept the books; that she didn't know he wasn't filing; that any money owed -- there has always been some withheld from her salary -- is being paid; that the anonymous leaking of the certificate of delinquency on Friday was underhanded -- indeed, it was -- and that she should still be elected to Congress. But it is illegal as well as wrong not to file a tax return. Whatever the right response to such a failure, it surely is not to reward it the next day with a seat in Congress.

Mrs. Norton and her husband are both lawyers, she the former head of a major federal agency, he the former chairman of the District Board of Elections and Ethics. They know about taxes. They have both been regulators, officials in the business of telling other people how to organize their affairs and of penalizing them for failure to comply. Mr. Norton now admits to "procrastination" in dealing with their D.C. taxes. What does that mean? Who gets to "procrastinate?" What really happened? We don't know. Can it really be that for eight years a debt that with penalties and interest could reach many thousands of dollars -- the claimed liability from 1982 alone is more than $25,000 -- built up and no mention was made of it in the family? Did Mrs. Norton never see even a notice addressed to Mr. and Mrs. from the District government seeking payment? Are the eight years of unsettled accounts with the District all of it, or is there more?

It may indeed be as Mrs. Norton has described it, but the questions aren't going to go away on the strength of the sort of statements she has made thus far, nor are they going to stop with Tuesday's election. The District is in no position to carry the extra load that she would put on it. She has indeed had the remarkable career her supporters say she has, and we hope it will continue -- but not in this job at this time. Mrs. Kane is the right choice.