A Coast Guard regulation went into effect Jan. 1 requiring anyone in a boat more than 16 feet long, or anyone in any boat on the water after dark, to carry a visual distress signal.

That's federal law. The Coast Guard lists three acceptable devices. The one that has proven to be the most practical and popular is the flare gun. So thousands of boaters have bought or are planning to buy flare guns. These gadgets are available at boat equipment shops and dealerships for as little as $10.

On fair days these boaters will go out on Chesapeake Bay or other Maryland waters. When they do they will be in violation of state firearms laws.

Mike Sciulla of BOAT/US, a boat owners' lobbying firm, explained it this way:

"Maryland state law defines a firearm as any device that propels a missle by gunpowder or similar explosive, so in Maryland a flare gun is a firearm. And Maryland law defines a handgun as any pistol, revolver or other firearm capable of being concealed on the person.

"So a flare gun is a handgun. Maryland law requires a permit to carry a handgun. Technically, anyone who carries an unlicensed flare gun on his boat in Maryland is in violation."

Catch-22: If he doesn't carry one, or some other acceptable visual distress signal, he is violating Coast Guard regulations. It's a sticky problem that Maryland officials are working to resolve. Assistant Attorney General Mike Scibinico said emergency legislation is being drafted that would exempt flare guns from handgun laws.

That legislation may or may not be passed in the current session. Meanwhile, Scibinico said, Attorney General Stephen Sachs has recommended no enforcement of the handgun laws as they apply to marine distress signal devices used on boats.

It was not without some concern that the state decided on that course. "These things are dangerous; there's no question about that," Scibinico said. "They're not like a bullet. They won't go through you. But they will burn. If you walked down the streets to Baltimore with a flare gun you'd be in violation of handgun laws."

Flare guns can do serious damage. On Jan. 14 a cook refused his captain's order aboard a Panamanian freighter docked in Miami. The captain shot the cook with a flare gun, critically wounding him with burns over 40 percent of his body.

The flare bounced off the cook's chest. The Coast Guard safety officer who investigated said, "He was lucky it didn't enter his body. I'm sure if it hit somebody at close range the flare would not only burn skin but the force of the shot would cause it to go into the body."

That is less true of pleasure boaters' flares than merchant vessel flares, which are more powerful than the recreational models. The approved merchant flare attains a height of 1,200 feet.

Flare guns sold to boaters come in smaller sizes, according to Tim Vanderver, a Washington lobbyist for the Pyrotechnic Signal Manufacturers Association.

Standard sizes are 25mm, which sends a flare about 375 feet in the air, and 12-guage, which attains a height of about 225 feet.

Vanderver said one manufacturer performed safety tests by firing the flares at chicken breasts. ("They tried to get people but no one would hold still," he said.) The tests showed the 12-guage shell generally did not penetrate the flesh. "They determined that on a human the shell would bruise but probably not penetrate," he said.

However, the flares burn intensely for six seconds and would do damage if fired at someone at close range, Vanderver said.

The problem is that flare guns are really the only rational marine distress signal alternative. The two other Coast Guard-approved gadgets are a hand-held flare, which introduces the worrisome element of open flame on the boat, and an electric light, which is expensive and useless in the daytime. t

Presumably some clarification of the Maryland law will come before the 1981 boating season arrives. Meanwhile, boat dealers are selling and boat owners are buying flare guns, regardless of the conflicting laws.

Most of them have safety in an emergency on their minds. A few are looking for double duty from their flare guns.

"Let me see that one," a man instructed a salesman at a booth in last fall's Annapolis In-the-Water Boat Show. The salesman handed him an orange plastic pistol with three 12-guage flares attached to a strap.

"I'm sailing down to the Bahamas," the man said. "I don't want to carry a gun, but if somebody tries to board my boat in the middle of the night I want to have something aboard to fight back with."

"This ought to do it," said the salesman.

So the boater paid his $12 and walked out with a little plastic pistol, his protection on the high seas.