WASHINGTON (AP) - Deer hunters and other sportsmen will have to pass an instant background check before they can buy a rifle or shotgun under a change in a federal gun law that takes effect Dec. 1.

The background check, done on the spot in the gun store, will be the first national screening of hunters, target shooters and others buying long-barreled guns and will be the same as the instant checks now done in many states on would-be handgun purchasers.

''They're trying to take away the people's freedom by pieces,'' complained Joe Garcia, looking over the shotguns at a Wal-Mart near Waldorf, Md.

Both sides in the perennial argument over gun control are girding for renewed friction as gun buyers like Garcia confront the new restriction.

Buyers of ''long guns'' were exempt from the Brady Act's requirement of a background check and five-day waiting period for handgun purchases when it passed in 1993 and took effect in early 1994.

That compromise legislation also looked ahead five years to a day when an instant, national computerized background check system would be in place, eliminating the need for the five-day waiting period and allowing the expansion of background checks to all gun purchases from registered dealers. That day is Dec. 1.

''There are going to be a few million mighty surprised hunters come Dec. 1,'' said John Velleco, spokesman for Gun Owners of America, a lobbying group opposed to gun control.

Until now, there was no comprehensive check on whether long gun buyers were telling the truth on federal firearms forms. The forms ask buyers whether they are felons or other groups barred by law from owning guns.

Eight states - Illinois, Massachusetts, New Jersey, Virginia, Florida, Pennsylvania, Connecticut and Delaware - already have some form of background check covering long guns, according to Handgun Control Inc., a lobbying group that pushed for the Brady law.

The law was named for presidential spokesman James Brady, who was wounded in the 1981 assassination attempt on President Reagan. It is most closely identified with the five-day waiting period for handgun purchases.

Handgun Control and the National Rifle Association, which rarely agree, do agree that the inclusion of long guns drew little notice when Congress passed the Brady law and even less since then.

''There appear to be quite a few people that have either forgotten about this or never paid any attention in the first place,'' said Tanya Metaksa, the NRA's chief lobbyist.

The issue is tricky for the NRA, which helped engineer the switch from a waiting period to the instant check system when the Brady bill was before Congress. The NRA regards the instant check as less onerous, since the vast majority of buyers will be able to walk out of the store with their guns instead of returning to pick them up later.

Garcia, of Brandywine, Md., knew the law will change but was unclear about the details, saying, ''If it's instant, that would be better,'' and would not keep him from buying a gun.

Gun merchants, who must explain the new system to prospective buyers, predict startled and angry customers.

''Unless they are pretty active in gun issues or very well-read, I bet you the overwhelming majority of gun owners are totally unaware this is going to kick in,'' said Steve Schneider, owner of Atlantic Guns in Silver Spring, Md.

The instant background check system will scan criminal and mental health records, military discharge rosters and other databases to see whether a customer may legally buy a gun. The system will not reveal why a customer has been rejected.

If it rejects a would-be buyer, it will put a ''hold'' on the sale, giving the store and customer three days to assess the problem. If the computer then rejects the buyer again, there is an appeal process.

Brady background checks blocked sales of some 69,000 handguns in 1997, more than half because the prospective buyer was a convicted felon or was under a felony indictment, the Justice Department says.

Long guns are used in relatively few crimes, despite the notoriety of recent schoolyard rifle shootings.