The Supreme Court again declined to consider a challenge to a state's ban on some semiautomatic weapons, boosting the hopes of gun control advocates who want President Bush to continue a federal ban.

The court's action Monday in a New Jersey case offers further proof that such bans are workable and constitutional, said Brian Siebel, senior attorney at the Brady Center to Prevent Gun Violence. He said President Bush should continue the federal ban that expires in 2004.

"In today's environment, where we are concerned about terrorism, it would be insane to allow civilians in America to buy military-style weapons," Siebel said.

But Greg Costa, a spokesman for the National Rifle Association, said bans like New Jersey's do not make communities safer.

"This law didn't cause criminals to disarm," he said. "Furthermore, there was never any evidence that criminals commit crimes with so-called assault weapons."

Bush said during his presidential campaign that he would reauthorize the ban on certain semiautomatic weapons, though groups representing gun owners might press him to reconsider.

Chuck Cunningham, director of federal affairs for the National Rifle Association's legislative wing, said he doubts the success of state laws will influence the debate over the federal ban as 2004 draws closer.

The Supreme Court's decision not to hear a challenge to New Jersey's ban on so-called "assault-style" weapons is the latest in a series of defeats for gun-ownership groups that consider such bans unconstitutionally vague. In February, the court passed up a challenge to California's 1989 ban, the nation's first.

Connecticut, Hawaii, Maryland and Massachusetts also have passed bans. Congress passed the federal ban in 1994.

The main point of contention has been how the laws define outlawed weapons.

New Jersey's law, passed in 1990, lists 37 models by name but also covers others that are "substantially identical." The intent was to keep gun makers from making tiny adjustments to banned weapons as a means to circumvent the law.

"If you don't have that type of language there, you can render the statute meaningless," said state Sen. William Gormley, a Republican who broke from party ranks to help draft and pass New Jersey's law.

California's law has been challenged five times over how it defines outlawed weapons. The state Legislature tried to address the issue in 1999 by adopting a provision that bans weapons based on a list of features, rather than a list of makes and models.

Other states have tried other approaches. Hawaii's 1991 ban uses a generic definition of outlawed weapons. Connecticut and Maryland banned weapons specifically by name.

The federal ban covers 19 designated weapons plus other firearms with specified features. The House voted in 1996 to repeal the ban but the Senate did not follow suit.

The challenge to New Jersey's ban was brought by the Coalition of New Jersey Sportsmen; Illinois-based gun manufacturers Springfield Inc. and Armalite Inc.; and several gun owners including Robert Viden Jr., a director of the National Rifle Association.

They said the phrase "substantially identical" offers inadequate direction to gun owners about whether they own a legal or illegal weapon. A New Jersey federal court and the 3rd U.S. Circuit Court of Appeals ruled in the state's favor, setting the stage for the appeal to the Supreme Court.

Shortly after the group filed its lawsuit in 1996, Peter Verniero, then New Jersey's attorney general, issued guidelines to help county prosecutors define the "substantially identical" provision.

Gary Needleman, an attorney who represents the plaintiffs, said even those guidelines did not clarify just which guns are covered.

"You have people prosecuted under a law that defies comprehension," he said.

Gun owners particularly dislike New Jersey's law because it applied retroactively to guns purchased before the law was passed.

Gov. Jim Florio, a Democrat, signed New Jersey's ban into law on March 17, 1990. Some state legislators tried unsuccessfully to overturn the ban in 1992 and 1993.

Statistics kept by the New Jersey State Police show a gradual reduction in the number of criminal offenses involving semiautomatic weapons, from 110 in 1991 to 70 in 1999.

The National Institute of Justice reported in 1999 that in the two years after the federal ban was implemented, criminal use of weapons covered by the law declined 20 percent.

The case is Coalition of New Jersey Sportsmen v. DiFrancesco, 01-120.