Lord, if my father could see me now," Tucker Brown shouted across the glinting Patuxent River.

Brown is a St. Mary's County waterman, as the men in his family have been for generations beyond counting. It wouldn't surprise his forebears that he's still wresting a living from the Chesapeake Bay and its tributaries. What would surprise them is the way he's doing it.

Brown stood aboard his 46-footer Frisky the other day, culling some of the prettiest, fattest oysters the Patuxent has ever yielded. But instead of having to dig for them with 18-foot hand tongs or heavy hydraulic patent tongs in the time-honored ways, he simply waited for two tugs on a line.

When the yanks came he looped the line over a block, took three wraps on a winch and hauled up another basketful of muddy shellfish.

Fifteen feet below was his oyster-catcher: not a computerized robot but something almost as revolutionary, a man bathed in warm water enjoying a peaceful, serene day's work on the river bottom.

This is the year Brown and a couple of hundred other Chesapeake oystermen have undertaken with great success a controversial new harvesting tactic, oyster diving.

Five days a week he and diver Roy Sprague head for the oyster grounds at first light. As they travel, Sprague checks his compressor and organizes the tubes and hoses that will sustain him underwater.

This week they were working close to home, and by the time the sun turned from red to gold, Sprague was climbing into his leaky dry suit.

"It's not a dry suit anymore," he laughed. "They all leak."

What keeps that from being a bitter nuisance is the gas-fired household water heater that sits just behind the cabin bulkhead. It's connected by a hose to the leaky dry suit, and all day long Sprague is bathed in 105-degree bath water as he works. When his bubbles come to the surface they bring steam.

The refinement of a comfortable heating system for the diver and trustworthy compressors that provide an all-day air supply have turned oyster diving into a major Chesapeake industry almost overnight.

Five years ago, about the only oyster diving in the bay was recreational--scuba divers who hired boats for winter dives and brought up the succulent bivalves for their own consumption.

But the recreational divers hired some watermen to take them out one day and it wasn't long before the watermen had seized on the idea. By the 1980-81 season, oyster divers accounted for 8 percent of Maryland's oyster catch (oystering being by far the state's biggest water industry). Last year the diving fleet included about 100 boats that produced 18 percent of the catch. This year state officials estimate that as many as 300 dive boats are operating and the percentage of dive oysters is certain to be take another leap.

The sudden growth sparked fear about safety and some complaints from traditional oyster harvesters. Last year the legislature established a 12-member task force to study diving. Their report, to be completed in a few weeks, is not expected to recommend major changes in the way divers work.

The safety concerns stem from the fact that three divers have died at work--one by drowning, one by asphyxiation and the third by heart attack--and there have been many more close calls, according to Pete Jensen of the state Department of Natural Resources. The task force probably will suggest safety measures, including mandatory classes and certification of divers.

Complaints from traditional oyster-gatherers are thornier. "The tongers claim the only reason we still have oysters in the bay is the laws that make harvesting of them difficult and inefficient," said Jensen. "They say diving is in conflict with that. There probably is merit to the argument that inefficiency prolongs the stocks, but it's hard to argue with a small-business man who comes up with a better way to do his job."

Jensen said he expects the task force to offer no "conclusive recommendation" on allocation of the resource, leaving that to the legislature. State Sen. Frederick C. Malkus (D-Dorchester) has indicated he will seek to set aside certrain oyster-rich areas of Dorchester and Talbot counties as no-diving zones in a pilot program, to see if oyster stocks there do better there than in waters where diving is permitted.

Brown, who shifted over to diving six weeks ago after a lifetime of tonging, agrees that the new technique is efficient, but he does not share the view that diving will deplete oyster stocks dangerously.

"We're catching oysters that have never been caught before," he said. Because the divers work deeper water than tongers can, he said, the dive boats are bringing in fat, older oysters, which, if they weren't caught this way, would die of old age.

"Just look at these oysters," said Brown as he triumphantly scattered another bushel onto his culling board. "You'll never see prettier ones. And he's leaving plenty behind. You can't catch them all. He's only taking the best ones."

Because of consistent high quality, dive oysters draw the highest price from shucking houses. Even after the price fell last week from $13 to $12 a bushel, Brown and Sprague were splitting close to $400 for an average day's haul of more than 30 bushels.

There are expenses. Sprague figures he has $2,000 invested in his diving gear alone, and things do break down.

His hot water, for example, is channeled through surgical tubing to his feet and hands and back. To keep the tubes in place on his legs he has sewn them into a pair of tights, which he dons before each dive.

"Last week he come out complaining," Brown reported. "He told me, 'Aww, I ripped my pantyhose.' "