D.C. election officials yesterday blamed an error-filled computer tape for election day problems that caused numerous ballot mix-ups and improperly kept some voters from casting ballots.

Board of Elections and Ethics chairman Albert J. Beveridge III also acknowledged that the city does not have an accurate master list of who is registered to vote here.

Neither Beveridge nor other city officials were able to explain how the computer snafu occurred.

"I don't know. I don't know," a frustrated Beveridge told reporters yesterday. Beveridge placed part of the blame on the city's central computer system, which he said was more than two weeks late in delivering the board's most recent list of registered voters to the elections office.

The list, which legally must be ready for public inspection two weeks before any election, was not delivered to election officials until Friday, Beveridge said. Other elections officials said the list was made available only after an urgent appeal to the office of City Administrator Elijah Rogers.

So tardy was the list's delivery that it was impossible to cross-check it for inaccuracies, according to election officials, who said clerks instead spent the weekend and Monday frantically duplicating the list and sending it out to the city's 137 precincts.

While Beveridge said he did not believe the outcome of any school board race was affected by the problems, he and other city officials warned that some of the 364 different contests for the Advisory Neighborhood Commission (ANC) and the 45 Statehood Constitutional Convention seats might be challenged. Many of those races were decided by small margins.

Yesterday, Manuel B. Lopez, who finished third in the 17-person race for two at-large school board seats, said he expects to challenge the results.

According to Beveridge, there remain uncounted about 4,000 ballots cast Tuesday. Most of those were cast by voters whose names did not appear on the computerized voter list. In addition, an undetermined number of absentee ballots also remain uncounted, he said.

Nonetheless, no city race has ever been determined by late-counted ballots.

Beveridge said officials knew in late October that there would be problems with the ANC races when some candidates for the hundreds of seats began reporting confusion over their district boundaries. In an effort to avoid the problem in the future, Beveridge said he would ask the City Council to certify the ANC boundaries well ahead of the next election. He said officials were still counting ANC ballots yesterday.

The elections board is in the midst of a massive switchover from using the city's central computer system to one the board will run itself, according to Beveridge. He said the City Council earlier this year rejected a suggestion from the elections board that the entire city be reregistered to bring up to date the city's files.

He said his office has on file about 1 million voter-registration cards, a number that far exceeds the city's population. Only about 273,000 of the cards are believed to be valid, Beveridge said.

According to Beveridge, until the elections office completes its sorting of the cards, discarding the invalid cards and entering into the new computer the valid ones, the city will remain without a single master list of registered voters. He said he hoped to have the task completed by early next year.

City Council member William Spaulding (D-Ward 5), saying the election "marred the face of our entire electoral process," announced yesterday that Government Operations Committee he heads will investigate the election problems and begin holding public hearings on the matter in 10 days.

Spaulding, vowing "all-out war" over the election problems, said the board had assured him before the election that there were "no possible foul-ups." He complained his committee had been "constantly thwarted" when trying to get information from the board members.