The lower Patuxent River looked less than inviting. The wind-whipped water was sinister gray, with a temperature of 38 degrees.

"You a bit apprehensive?" Dave Sommers wondered as we stood hands in pockets at a pier, across from Solomons Island near the western edge of the Chesapeake. My pant-legs fluttered in a 10-knot breeze.

"I think I'd be foolish not to be."

"Well, at least you're honest," Sommers said with a grin. "I could tell you're a little nervous. You have that. . . look."

It was a Saturday in winter -- a fact that worried him not a whit as he stuffed himself into a wet suit and helped me do the same. Soon we'd be shuffling backward through a foot of chop -- backward, because you can't wade forward with flippers on -- and plunging to the bottom for an oyster dive.

Diving for oysters, for fun not profit, is a pastime belonging to a subculture of scuba. The regulars hereabouts, active from September through March, are a hardy crew. They'd just as soon get cold as wet because the oyster's their world.

"You might say we're crazy," cackled Jim O'Brien, an accountant for the Securities and Exchange Commission. He was among about half a dozen divers who took a long walk off the short pier and climbed out later with a bushel of bivalves.

Such recreational oyster-hunters, who've plied their hobby only since the early '70s, account for a tiny fraction of the total Maryland harvest -- which in 1980 amounted to 21/2 million bushels. Bill Outten, director of the shellfish program for the Maryland Tidewater Administration, says recreational divers are permitted a bushel per diver per day (compared to the 25 bushels allowed commercial divers and oystermen), and mustn't take oysters of less than three inches in length.

"As a general rule of thumb, oysters grow about an inch a year," he says. "So it takes a minimum of three years before it gets from being a spat to the point where it can be harvested legally."

That day on the pier, sheltered in Sommers' car, I struggled the better part of half an hour -- I was in no hurry -- to don the tight-fitting wetsuit from Sea Ventures Dive Shop in Fairfax. The shop, for which Sommers teaches when he's not crime-solving with the Fairfax County cops, runs Saturday-morning oyster trips to the lower Patuxent at Solomons, about two hours from Washington.

"The thing about harvesting oysters," says Ron Pitts, Sea Ventures' owner, "is that you first have to have access to them, then you have to know where they're at, and then you have to know what they look like. A surprising number of people don't know what oysters look like. They end up bringing back a bunch of rocks." After anguishing over my lack of experience -- a week of scuba long ago -- Pitts let me dive under Sommers' supervision.

So we stood poised on the riverbank, a vision in black rubber. Aside from the basic suit of head-to-toe neoprene -- which, with mask and regulator, bares a square inch or so of skin -- we also wore lead weightbelts and inflatable buoyancy compensators, while Sommers had attached to himself a daunting array of knick-knacks: depth gauge, compass, thermometer, writing slate, catch bag, float bag, knife and, with a 20- foot line, a flag-buoy to ward off boats from our position.

"Okay, let's do it," Sommers said brightly as an icy gust swept over us.

It was just after noon, and the tide was coming in. I took a last look at the lapping soup and grabbed hold of a piling, lowering myself in to the kneecaps. The wetsuit lets cold water in, and body heat takes care of the rest. It felt chill through the porous neoprene, but not so cold as I'd feared. Only my rubber-gloved fingers were getting stiff. Sommers handed me the flippers placed the airtank on my back and, as I spit into my mask and washed it out jumped in tank and all -- some 80 pounds of gear.

We did an about-face and started out, my teeth clenched to the mouthpiece of my regulator. ''You're breathing like a racehorse,'' Sommers said.We trudged beyond the pier into the rising tide, and each few yards made for a new level of gooseflesh. When the water reached our necks, we twisted around and dived.

Holding onto Sommers' nylon-mesh oyster bag with my left hand, I pinched my nose with my right and kicked toward bottom. The water, more buoyant than I'd bargained for because of the salt, was murky-green through my mask. Sommers grabbed my arm and gave me a downward tug. I caught sight of the sandy bottom about a foot from my face. After a moment, I realized I'd lost a flipper.

"Well, that's it," Sommers sighed when we surfaced. I gulped saltwater in reply. "You can't dive with one fin. Let's go back."

The dive had lasted 20 seconds, and now we were oysterless, making for shore. I was disappointed, a tad embarrassed -- and greatly relieved -- as we hit the pier. "Hey, you guys! Where you been?"

That was Paul Kellam, a diving buddy of Sommers. He'd just driven up to the riverbank, and happened to have an extra pair of fins, my size. He handed them down. I dutifully put them on and off we went once more.

This time we went under for a good 20 minutes, swimming along the bottom against a light current. Every so often, Sommers tossed something into the oyster bag, but most of the time he was watching me -- probably to assure himself I wasn't about to drown. As it turned out, I was starting to have fun.

No longer cold, I followed rock-strewn rivulets of sand along the riverbottom, my mask brushing up against swatches of eel grass. There wasn't much to see -- or at least, with two feet of visibility, I didn't know what to look for -- but there was a heady feeling of floating, as if in outer space.

Sommers nudged me and pointed to a rough-textured stone suspended off the bottom. He prodded it with the rim of the oyster bag, and what I'd thought was a stone suddenly became a berserk oyster-cracker fish, stretching its jaws to a threatening angle before swimming away. My breathing, which had slowed to a trot, promptly resumed its race-horse rhythm as I backed off in surprise.

When we climbed ashore, Sommers dumped from his bag a couple of rocks and half a dozen oysters. A few yards away, a contingent of the Free State Scubanauts, a diving club from Rockville, sorted through their own catch: bushels and bushels aplenty.

"I was paying so much attention to you," Sommers said with a rueful smile, "I didn't have much of a chance."

We peeled off our wetsuits and donned dry clothes -- Sommers with dignity, while I howled at the wind -- and then Sommers shucked our catch. He tended to a sliced thumb, the inevitable result of oyster- shucking, as I greedily slurped them down.

"Want one?" I offered.

"Naw," Sommers said, before we repaired to a beer joint opposite the pier, "I don't really like 'em raw."

DIVING FOR OYSTERS

Sea Ventures Dive Shop arranges oyster dives most Saturdays throughout the winter -- from a boat if the weather's calm. The trip-leaders require you to know the basics of diving, and offer certification courses, which can cost from $95 to $125, excluding equipment rental. Call 703/425-7676 for information.