The steadiest traffic jam in Arlington may have been inside the county courthouse Monday, as the deadline for displaying county tax stickers on cars arrived and residents filled the corridor outside the treasurer's office to pay their personal property levies.

County officials had extended the deadline for displaying the gray stickers, which indicate payment of 1984 taxes, from Sept. 17 to Oct. 1 and then to Oct. 15, citing breakdowns of the county's computer system and repeated post office tangles that delayed the decals' arrival.

When the grace period ended at midnight Sunday, Arlington police began ticketing cars without stickers, according to County Treasurer Frank O'Leary.

"It's been zooey today," said Chief Deputy Treasurer Kevin R. Appel, as he rushed about his office, answering the phone and calming irate taxpayers. "Today's been steady. I haven't had lunch yet," he said at 4:45.

To complicate the mess, Arlington real estate taxes, paid twice a year, were also due yesterday, and county sheriff's deputies began at dawn to seize the vehicles of some longtime delinquent taxpayers.

About 500 people streamed through the treasurer's office all day, according to Appel. "It's been a banner day," O'Leary said.

Police said the total number of cars ticketed for not displaying decals would not be available until later this week. The tickets are $10 for parked cars and $30 for moving vehicles, including court costs, according to the county magistrate's office.

O'Leary said the computer and postal problems that prompted him to extend the deadline were solved about two weeks ago. While some decals may have been lost in the mail, he said, "Most of the people who are receiving tickets now deserve to do so."

O'Leary, who made his planned crackdown on delinquent taxpayers a campaign issue last fall, began this spring to seek out citizens who owe the county about $5 million in back taxes. Seizing vehicles, which began at 6 a.m. Monday, was the final step, he said.

"We have an extensive list -- we are focusing on 98 vehicles as our immediate target," he said.

Sheriff's deputies said that of nine vehicles seized Monday, four remained late Monday afternoon in a county lot in South Arlington.

The treasurer's office remained open past the usual 5 p.m. closing, but by 5:30, the line had dwindled to three or four people.

Dee Waterloo said she was surprised when a police officer pulled her over near her home on Barton Street. "It was really strange," she said. "He told me the decal was up yesterday (Sunday)."

Waterloo said that although she had been waiting in line for about 20 minutes, was missing work and suffered from a sore throat and a fever, "I'm not irritated. They have to do something when the stickers are up."