Thousands of Washington voters began receiving letters last week urging them to reregister with the D.C. Board of Elections and Ethics within seven days or face being "canceled" from the regular voting rolls.

Elections officials, who have since sent out more mildly worded letters, said yesterday the mailing represented an attempt to clear up the board's tangled election records. Despite the wording of the first letter, they said, no one will be disenfranchised.

Teddy Filosofos, the board's recently hired elections director, said the letters were sent after it was found that thousands of voter registration cards are missing from the board's master file.

He said he does not know more precisely how many cards are missing, nor does he know why they are missing. Those who attempt to vote in the Sept. 14 primary election and are found not to have registration cards on file will be allowed to vote by special ballot, he said. Special ballots must be reviewed individually by the board.

The initial letter, which came at a time when many Washingtonians are leaving the city for vacations, confused many voters and drew complaints from many others, elections officials said.

"My responsibility is to make sure all the voting lists of the people registered in Washington, D.C. are accurate so we don't have the same problem we had in 1981, when people were arbitrarily told they could not vote," Filosofos said in explanation of the letter.

He has revised the letter twice. The most recent version states that those who do not comply will have to vote by special ballot.

Last November, thousands of D.C. residents had difficulty voting and thousands of others were left off the voting rolls. Earlier this year, a City Council committee concluded that as many as 50,000 people were not properly accounted for in the board's voting records and could have trouble voting in the primary.

More than 60 people have been hired to pore over voter lists this month, matching names with corresponding registration cards. If a card is missing, a registration application is mailed to the affected voter.