Property tax bills went out to 5,900 D.C. homeowners last week bearing the alarming but erroneous news that their payments were late for the first half of 2005 and that the city was charging them penalties and interest.

District tax officials blamed the mistake, which added a 10 percent fine and two months' interest to each bill, on a computer glitch that has been corrected. They said revised bills with the correct numbers should start showing up in the mailboxes of affected homeowners this weekend.

"Most property owners don't have to do a thing," said Martin Skolnik, director of the city's Real Property Tax Administration. "We're just sending them a new bill so they can see the right number and verify that they don't have to pay penalties and interest."

As far as city tax officials have been able to determine, the mix-up affects only customers of Countrywide Financial Corp. and First American Real Estate Tax Service. Among the more than 200 mortgage companies that pay property taxes for District property owners, Countrywide and First American alone failed to pick up on the city's new system for matching properties with tax bills, Skolnik said.

The city sent the companies a new set of "document control numbers" in mid-March, in advance of the March 31 due date for the first half of 2005. The companies sent the payments by the deadline, Skolnik said, but failed to use the right control numbers, causing the tax bills of 5,900 homeowners to enter computer limbo.

The city quickly recognized the problem and asked Countrywide and First American to correct it. The companies resubmitted payment information using the new control numbers in mid-May. Unfortunately, Skolnik said, a computer programmer assigned to match the previously received cash with the newly received control numbers recorded May as the date the payments were received, erroneously adding a 10 percent penalty and two months' interest to 5,900 tax bills.

Skolnik said customers of other mortgage companies should also check their tax bills closely.

"If other people have this problem and they know they paid on time, they need to call our customer service line so we can fix that individually," he said. The number to call is 202-727-4829.