Carr's and Sparrow's beaches on the Severn River have been abandoned for years, victims of changing times and revised gambling laws. Instead of shouts from frolicking bathers and slot-machine winners, all you hear these days are the throaty whistle of a quail in the woods or the croak of a blue heron surprised in mid-hunt.

Yet there are fortunes still to be won in these forgotten places, Bob Trevillian will assure you.

Trevillian, 29, and partner Frank Carter are underwater treasure hunters.

They do not wear Scuba tanks nor do they study pirate maps where X marks the spot. They go instead to deserted Chesapeake Bay beaches, poke around in the shallows with waterproof metal detectors and often come home with gold and silver.

Sometimes they are scorned as "garbage pickers," chuckled Trevillian. They can laugh at that, he said, because for about seven years he and Carter have supported their families very nicely by treasure hunting, mostly at beaches. Lately they've upped their earnings by publishing two books on the subject, Treasure on the Chesapeake Bay and Diamonds in the Surf, and opening Spyglass Enterprises, a treasure-hunting shop.

At home and in the tiny, pin-neat shop in Glen Burnie, they have boxes upon boxes of coins, medallions, trinkets and jewelry. Much of it is junk, but some is precious metal; every once in a while they stumble on a nice sparkly diamond.

The good stuff they take to be appraised at Sanders' Keepsake Jewelers, where they hurried two years ago when Trevillian unearthed a diamond ring at Fort Smallwood Beach near Baltimore.

"It was 2.35 carats--not a high-quality stone--and an older, European cut," said Lawrence Sanders. Still, the jewelers appraised the ring at $13,500, a replacement cost that is about twice what the ring actually might bring on the open market, Sanders said.

The men dashed over to Sanders' again last week when Carl Harrison, a regular colleague on water hunts, dug up a 40-year-old platinum and diamond dinner ring from a southern Anne Arundel County beach. The stone was just over half a carat and the ring was appraised at $3,500.

A few mornings later when the three men took a novice hunting at Sparrow's Beach, within sight of the State House in Annapolis, no one expected Harrison to find anything.

"I've got the three-day syndrome," said the former newspaper delivery agent. "Any time you find a diamond, for the next three hunts you get nothing."

The men parked their van on a litter-strewn dead end, donned wetsuits, gathered up metal detectors, hand diggers and sifters and trundled 200 yards down a weed-choked trail. On their right stood the remains of the old beach turnstiles, where 30 years ago Washingtonians paid for a day of swimming; on the left were the decrepit remnants of a wooden concession stand.

"Bob-WHEEEET," sang the quail.

Chesapeake beaches are good for treasure hunting because they are generally empty, now that Ocean City is only three or four hours from Washington, and because they stay shallow a long way out. The hunters generally don't work beyond waist depth, which is where Trevillian was, 50 yards from shore and 20 minutes into the morning's search, when he shouted, "Got one."

The steady "click-click" of his detector had speeded briefly. Trevillian zeroed in on the metal; with a long-handled digger he scooped three or four times, pouring the sand and clay mix through a floating chicken-wire sifter. The gold shone brightly against the galvanized wire.

It was marked "Cardozo High School, 1953"--a class ring no doubt lost by some Washington teen-ager who arrived sweaty from the drive, dove carelessly into the cool water and never felt it slip off. It was marked 10k; approximate scrap value, $50.

By the time he quit four hours later, Trevillian had turned up a 14-karat gold 1929 Cardozo class ring; a silver ring so thin it was worthless; a gold-filled charm ring, a silver initial ring and a silver friendship ring, each worth a few dollars; a Mercury dime, a Roosevelt dime and a silver Washington quarter; four war nickels (40 percent silver), four buffalo nickels worth $1 apiece, three Jefferson nickels, three "wheat pennies," a brass skeleton ring and a small brass religious medallion. He'd also found a handful of bathing-cap snaps, bathing-suit clips, fishing rigs and other metal trash. Total value, about $125.

His partners each found a gold ring, including one from Washington's now-defunct Armstrong High, but fared less well overall, gathering $40 or $50 each in scrap and coins. "But you never know when that diamond is going to show up," said Harrison.

Trevillian and Carter maintain that they pioneered shallow-water treasure hunting, starting a decade ago with land equipment and improving it as they went along. They say there now are 35 or 40 serious water hunters around the bay, each with about $700 invested in equipment.

Trevillian, who gave up a real estate and insurance business seven years ago to hunt full time, said the treasure supply is holding up. Even beaches that are picked over replenish themselves with the winds and tides, he said.

But, thanks largely to him, the pressure on the sunken treasure troves is building. "We've seen guys who will sleep in their cars, hunt every tide, not come home for days," Harrison said.

"They get greedy," said Trevillian. "This gold and silver does strange things. It goes to people's heads . . . ."