Neon-blue sparks leap from two tiny metal prongs at the end of what looks like a pocket calculator, and Don Pruitt jolts forward, his knees buckling and his sagging frame supported only by the Howard County sheriffs who are grasping each arm.

"Boy, that one burns," says a stunned-looking Pruitt, himself the county's chief deputy sheriff, who has volunteered to be shocked for a videotaped demonstration of the device.

Called a Nova XR-5000 stun gun, the black plastic device, powered by a nine-volt battery, packs a 50,000-volt punch when pressed against a body, causing a person to lose neuromuscular control and collapse.

"It felt like a whole bunch of bee stings at one time," Pruitt said later, reviewing the videotape on which his twin brother Dennis, also a Howard County sheriff, stuns him eight times.

"You're conscious of what's going on, but all of a sudden you find yourself on the ground," said Conley Giles, a vice president of Nova Technologies in Austin, Tex., which manufactures the stun gun. While a jolt of three seconds can immobilize a person for several minutes, he said, the only long-lasting effect is a pair of red marks resembling mosquito bites where the prongs make contact with clothing or flesh.

The Nova stun gun -- the most popular of several similar shocking devices -- is the latest addition to the arsenals of police departments across the country that are seeking a nonlethal means of subduing unruly suspects, particularly those who are deranged or high on violence-provoking drugs such as PCP.

At a suggested retail price of $69.95, it is also becoming the weapon of choice for private citizens who feel the need to carry a weapon but are wary of handguns. The sale and possession of stun guns is legal in Maryland -- except for Baltimore City, which banned the devices last week -- and in Virginia, but barred in the District, where they are classified as dangerous weapons.

In the two years the Nova has been on the market, Giles said, more than 100,000 have been sold, half to police, the rest to private citizens.

Supporters of stun guns praise them as a less drastic alternative to weapons such as guns or even nightsticks. "Your 3-year-old kid can't get hold of a stun gun and kill himself or his playmate," noted Barbara Lautman of Handgun Control Inc. " . . . I'd rather have someone attack me with a stun gun than with a .44 magnum."

But the weapons have come under fire in recent weeks as offering the potential for abuse in both public and private hands.

In New York, five Queens police officers from what tabloid newspapers there quickly dubbed the "torture precinct" were indicted Thursday on charges that prisoners in their custody were repeatedly assaulted and burned with a stun gun.

In one of the cases, a teen-ager accused of selling $10 worth of marijuana charged that police stunned him repeatedly during a 20-minute period and threatened to apply the device to his testicles before he gave them a false confession.

The New York incident was not the first time in which stun guns have been the subject of charges of misuse by police officers. A former San Antonio deputy sheriff was convicted this year of a civil rights violation for using a stun gun on a handcuffed prisoner. And departmental charges of using excessive force are pending against a Maryland State Police trooper accused of shocking a handcuffed prisoner.

Responding to concerns about the safety of the guns and the possibility of private citizens abusing them, the Baltimore City Council voted unanimously last Monday to ban private purchase or possession of stun guns, joining six states -- Florida, Hawaii, New Jersey, North Dakota, Michigan and Wisconsin -- where the devices are either prohibited or limited to police use. Bills to restrict or probibit them are pending in Illinois, Louisiana, New Jersey, New York and South Carolina.

"The potential for misuse outweighs the possibility of good," said Baltimore City Council member Donald G. Hammen, who introduced the measure to ban the guns there. "If a little old lady has it and some big brute breaks into her house, chances are he will take that thing away from her."

Cary Young of Nova's "legislative team," formed about three months ago to combat the wave of anti-stun gun proposals, dismisses such legislation as ill-informed overreaction.

And the New York incident, said Nova's Giles, is testimony to the stun gun's value as a nonlethal weapon. "I don't think you can name another time when somebody has been abused by law enforcement 42 times and doesn't suffer any severe injuries," he said.

More than 300 law enforcement agencies nationwide are using stun guns, according to Giles.

Of area police and sheriffs, only the Prince George's County Sheriff's Department currently uses the Nova stun gun, although the Montgomery County Sheriff's Department stocks a close cousin, The Source, a flashlight with electrical prods at the end. Several local police and sheriff's departments employ a related device, known as a Taser (an acronym for "Tom Swift and His Electric Rifle," its inventor's favorite book), which achieves the same result with tiny electric darts fired at suspects from up to 15 feet away.

Fairfax County police are evaluating stun guns, according to spokesman Warren Carmichael. Maryland State Police recently received six of the devices for testing, said spokesman Bill Towers. Gary Abrecht, director of planning and development for the District police department, said that police have attended demonstrations but have not decided whether to buy.

Meanwhile, sales to private citizens are booming. Nova's market research indicates that many customers are employes who work late hours, and men buying them for their wives, Giles said. A number of gun stores, both here and elsewhere, report a surge in interest in them in the wake of the New York incident.

"It's a good alternative," said Carl Roy, owner of the Maryland Small Arms Range in Forestville. One customer who had been raped in her town house wanted something for self-defense and "ended up buying one of these," he said. "It gave her some peace of mind."

As stun guns proliferate, additional questions are being raised about their effectiveness and safety.

At the Dallas police department, which has been using 60 stun guns on loan from Nova in a pilot project, officers initially found that the guns generally "worked very well," said Sgt. Gail Daniel. Citing one example, she said, "At the end of the fight, the officer was not injured and the prisoner was not injured," she said.

However, she said, for still unexplained reasons, the effectiveness of the devices dropped precipitously, from 70 percent to 40 percent, after the first two months of use and has stayed low, even after Nova exchanged the old stun guns for new ones, prompting the department to consider ending the study before its scheduled conclusion in August.

"They're still putting out an electrical charge, but not one that's incapacitating the subject," she said. "That's the opposite effect from what we wanted. We wanted to keep the officers from getting hurt."

On the issue of safety, Nova's promotional videotape promises that the device is "completely safe," and Giles said the company is convinced of that, although it conducted no testing on humans before marketing the gun.

Dr. Robert Stratbucker, an electrophysiologist at the University of Nebraska Medical Center, studied stun guns for the Douglas County, Neb., sheriff's office. He tested the device on miniature swine, connecting the gun directly to the inside of the animal's heart, which closely resembles a human heart.

He said he found that "it was impossible to cause any abnormal rhythm disturbance," meaning that the device would be "quite safe" to use, even on those with pacemakers or heart disease.

But Dr. Justin McArthur, a neurologist at the Johns Hopkins Hospital who tested the device on Deputy Sheriff Pruitt, said he believed the stun gun needed additional testing to look at such issues as its long-term effects, the impact of repeated shocks, and its safety when used on epileptics or pregnant women.

No change was recorded in Pruitt's heart or brain waves after two shocks, McArthur said, but the sheriff experienced a temporary increase in heart rate and felt passive and lethargic after the shocks.

McArthur said he "would absolutely not recommend" that the device be applied at the base of the neck, where Nova says it is most effective.

"If they're so convinced it's safe, why don't they get together 10 of their salesmen and subject them to 20 shocks each," he said. "If this were a medical device, an artificial hip or articial kidney, there would have to be years of testing, thousands of pages of reports, animal subjects, even for the most simple device."