Some Fairfax County taxpayers who think they have pulled a fast one on the county will soon be in for a surprise.

Fairfax residents or former residents who have neglected to pay the county personal property taxes for their cars, campers and boats will find the money deducted from their state income tax refunds.

Fairfax officials said they have turned over to the state a computer-generated list of 16,796 delinquent personal property taxpayers who owe the county about $3.2 million from 1981, 1982 and 1983. The average debt to the county is about $190, the officials said.

A state official said yesterday that the county is likely to recover only about 2 or 3 percent of the $3.2 million in the first year of the program. But, he added, counties will be able to recover back taxes from the program in future years as well.

The personal property tax rate in Fairfax is $4.80 per $100 of assessed value. So, the annual county tax on a car assessed at $5,000 is $240.

The state plans to notify Fairfax and other Virginia counties if an individual who owes back taxes to the county is entitled to a state income tax refund. The county will then write to the taxpayers whose refunds will be intercepted, informing them of the action.

"We see this as being a real positive approach as a collection tool," said James E. Sandifer, assistant director of finance in Fairfax.