The National Rifle Association has long been viewed on Capitol Hill as a lobbying juggernaut, time and again crushing efforts by gun-control advocates to impose tighter restrictions on handguns and other firearms.

But as the two sides gear up for battle again this year, the vaunted gun lobby has been showing cracks within its ranks. Amid a sharp decline in the group's membership and a series of legislative defeats in key statehouses, conservative activitists are mounting a campaign to seize control of the 120-year-old NRA and purge its leadership of alleged "moderate" influences.

"The NRA has become a toothless dinosaur," said T.J. Johnston, a self-styled "gun radical" from Los Angeles who is running on a dissident slate of candidates that announced for the NRA board of directors last week. "There's been a kinder and gentler NRA that has led to this wash of anti-gun hysteria across the nation. . . . We need to have a meat-eating NRA that won't be kind to any legislator who votes against the citizens' right to keep and bear arms."

The complaint is not entirely new. For nearly 15 years, activists like Johnston and the NRA's Washington leadership have sharply divided the association, producing endless rounds of palace intrigue, firings of top officials and angry debates at annual conventions.

Much of the dissidents' ire, moreover, has been directed at the NRA's executive vice president, J. Warren Cassidy, who, as the critics see it, has been too accommodating to members of Congress and directed too much of the group's $87 million annual budget into innocuous "sportsman's activities" rather than into aggressive political action and lobbying.

"He's been referred to as the Monte Hall of the gun movement -- he's the guy that plays 'Let's Make a Deal,' " said Neal Knox, a Washington lobbyist who once was fired from the NRA and is spearheading the dissidents' campaign.

But NRA watchers say this year's rift has taken an unusually nasty turn. Cassidy, who declined to be interviewed, unleashed a stinging personal attack on Knox in the current issue of the NRA's American Rifleman magazine, which also contained ballots for the upcoming board of directors election.

In an "open letter to NRA members," Cassidy wrote that Knox's attacks on the NRA leadership were designed "for his own enrichment" and "to build his own lobbying business," which he said is a competitor of the NRA's Institute for Legislative Action in representing the rights of gun owners on Capitol Hill.

"That was a low blow," said Knox, whose firm, Neal Knox Associates, lobbies for a disparate group of independent gun groups called the Firearms Coalition. "If I'm doing this for my own enrichment, I'm not doing a very good job. My gross operating budget isn't much more than {Cassidy's} salary" -- a figure Knox placed at around $100,000 annually.

For many outsiders, particularly the NRA's critics, the gun lobby's internal struggles seem puzzling, if not inexplicable. While dissidents like Knox charge the NRA with going soft, gun-control advocates say the group has remained as uncompromising and ornery as ever.

Not only has the NRA defied the pleas of big-city police chiefs and remained adamantly opposed to controls on military-style assault weapons, but the group recently asked the Supreme Court to overturn a federal ban on the sale of fully automatic machine guns to individuals. The court decided not to take the case yesterday, dealing a setback to the NRA's argument that such restrictions violate the Second Amendment to the Constitution.

"Any organization that in the face of a record number of homicides in this country is advocating allowing access to machine guns in civilian hands seems pretty extreme to us," said Susan Whitmore, spokeswoman for Handgun Control Inc.

But the NRA dissidents believe their movement is gaining momentum, fueled by rising grass-roots anger at the gains made by gun-control forces. Their most dramatic example comes from California, where a new law requiring the registration of semiautomatic assault weapons produced widespread protests and "civil disobedience" last month among gun owners who refused to comply.

Johnston, a studio production coordinator for ABC-TV's "General Hospital" and the chairman of a protest group called the Gun Owners Action Committee, said that only about 18,000 of the estimated 300,000 assault weapons in the state were registered by the Dec. 31 deadline.

"People are getting very emotional about this," said Johnston, who added that he owns a "streetsweeper" and another assault weapon that he has refused to register. "I'm encouraging all gun owners in California to openly defy and resist the law."

One sign of disaffection with the NRA, the dissidents allege, has been an abrupt dip in the group's membership. An internal report provided to the NRA's membership committee last September showed that enrollment dropped by more than 120,000 during the first eight months of the year, bringing total membership to about 2.6 million -- down from a peak of about 3 million in the mid-1980s.

The decline came despite 51.3 million pieces of mail sent out by the NRA during this period, including 19.5 million membership promotions that included such offers as free "shooter's caps" and "Win a Winnebago" sweepstakes, the report shows.

Cassidy, in a letter to The Washington Post last week, blamed the drop on the recession, saying similar declines are affecting other organizations. He also noted that the NRA "successfully lobbied the 101st Congress to defeat every piece of legislation hostile to honest gun owners" last year.

For the dissidents, that is not enough. Johnston argued that the NRA must take a "pro-active" stand that seeks to advance the rights of gun owners. One example: a new federal law that would allow for a universal gun permit that would give citizens the right to carry concealed weapons. Such a law would undercut many local gun-control laws, including those in the District.

Why the need for such a law? "There's a lot of people dying out there because they're disarmed," Johnston replied.