Fairfax County supervisors yesterday banned their police department's cost-cutting practice of trading seized guns back to gun dealers. The weapons will be destroyed to ensure they don't return to the hands of criminals, board members agreed in a unanimous vote.

The board also prohibited the department from exchanging used service weapons for new ones, a practice that has become highly controversial since a gun that once belonged to a police department in Washington state was allegedly used by Buford Furrow in the assault on a Jewish community center in Los Angeles this summer.

Yesterday's changes give the Fairfax County Police Department the most restrictive policy in the region when it comes to disposing of guns. Most other counties and cities destroy seized guns but routinely exchange older police weapons for newer ones.

Fairfax Board of Supervisors Chairman Katherine K. Hanley (D), who proposed the bans, said she was acting to protect citizens by limiting in a small way the supply of guns on the street.

"I believe that Fairfax County residents have a right to believe that guns seized by police should be returned to their legal owners or destroyed," she said. "Law enforcement guns that are not useful any longer will also be destroyed."

Fairfax police said yesterday the county traded 555 seized guns between 1996 and 1999 in exchange for a lower price on newer weapons that are used by officers. An additional 100 guns were slated for trade but never were exchanged, police said.

Police Chief J. Thomas Manger said yesterday that he supports the new policy. But he said the cost of buying new service weapons for a force of more than 1,000 officers will be higher without the ability to trade in older weapons. A typical police gun costs $750, he said. Rearming the entire force might cost more than $750,000.

"When the time comes, the board is going to have to understand it might bear more significant costs," he said.

Manger also said he doesn't believe the new ban will stop gun crimes from being committed because weapons are too easily available. But he said he supports the board's action.

"It's symbolic," he said. "But it is a significant message that needs to be sent. What if one of our guns had been used in a crime? Can you put a price on that? No."

In fact, one of the seized weapons traded by Fairfax police to a dealer later turned up at a Richmond crime scene, according to documents analyzed by The Washington Post.

Representatives of Handgun Control Inc. praised Fairfax supervisors for their actions. Spokeswoman Nancy Hwa said stopping the practice of trading police weapons and seized weapons is a good idea.

"No single method is going to solve crime," she said. "There are definitely other measures that need to be taken to reduce gun violence. But it's a step."

Others are not so sure.

Fairfax Supervisor Michael R. Frey (R-Sully), who voted for Hanley's motion, nonetheless called it an election-year proposal aimed more at getting votes than at stopping crime.

"You are two months out from an election, so how are you going to vote against it?" Frey asked. "But in the public's mind, I don't believe [trading in police weapons] is something we should be doing."

Jim Manown, a spokesman for the Fairfax-based National Rifle Association, said his chief concern is that guns stolen from law-abiding citizens and then seized by police are returned to their proper owners.

Fairfax officials said the new policy will allow that.

But Manown said he doubts that the county's new policy will make any difference in reducing crime.

"It's an issue for the taxpayers of Fairfax County," he said. "One of their resources is being discarded that could benefit their police."

In other action, the board voted yesterday to use part of its $19 million surplus to set up a "rainy-day fund" that could be used to stabilize the budget if the county, one of the country's wealthiest and currently flush with cash, runs into another economic downturn.

The move to establish a $60 million "revenue stabilization fund" reflects a concern among some county officials that the current economic boom cannot last indefinitely.

"Many economists . . . are warning that the economy is showing signs of slowing," County Executive Robert J. O'Neill Jr. said in a memo to the board last week.

Supporters of the fund say it makes sense to use budget surpluses to avoid a repetition of the early 1990s, when a recession forced the county to cut spending and raise taxes.

Under the plan, annual contributions would be at least 40 percent of any surplus, and the supervisors allocated $7.8 million to the fund as a down payment. O'Neill said the account could be fully funded in three to five years.

The board rejected a proposal by Robert B. Dix Jr. (R-Hunter Mill) to require a two-thirds vote of the supervisors before money could be withdrawn. He described the proposal as a "lockbox provision" to ensure that the fund could not be used as a "piggy bank" to cover shortfalls.