A dank and miserable day dawns, with the waterborne world a palette of misty grays. Waterman Kenny Keen sets his boat, the Long Shot, over an oyster bar for a day of hard labor under a January rain.

Never mind the chill and the gloom; Keen is pleased to be out on Chesapeake Bay. For he is harvesting oysters, a catch depressingly rare in recent years.

"This isn't too bad," Keen says appreciatively as he sorts through shells pulled aboard by patent tongs, a type of powered rake. He well remembers seasons with oysters so scarce it made no sense to burn time or diesel fuel looking for them.

Those lean years may be drawing to a close. For the first time since the bay's oyster population crashed more than a decade ago, watermen, scientists and others are guardedly optimistic that the shellfish may be rebounding.

Such a recovery would signal important progress in the long-running campaign to clean up Chesapeake Bay, North America's largest estuary. And an oyster resurgence would poise the bay for greater gains, since the bivalve is a voracious filter feeder that sucks pollutants from the water.

"It's a critical role that we haven't had in the bay for 20, 30 years," said William Matuszeski, head of the Chesapeake Bay Program, a federally led regional partnership to restore the estuary. "If we can get it back, we'll start getting the bay to begin working on its own cleanup."

Reasons for optimism are not hard to find.

Maryland watermen such as Keen are in the midst of a relatively strong harvest, the second in two years. New survey results indicate that the oyster population may be shaking off lethal disease epidemics.

Top political leaders of Virginia and Maryland are poised to commit their states to a tenfold increase in oyster populations. And Maryland Gov. Parris N. Glendening (D) wants to double spending on oyster replenishment, pledging $25 million over 10 years.

Nobody is predicting that oysters will regain their astonishing abundance of a century ago, when reefs of oyster shells jutted above the bay's surface at low tide, posing hazards to navigation.

But many in the oyster business--including watermen, biologists and state officials who monitor the shellfish--say the creature could reclaim important ecological and commercial roles.

"There is a much more heightened sense of optimism compared with a few years ago, when everything was characterized by despair," said Bill Goldsborough, a senior scientist with the Chesapeake Bay Foundation, a private conservation group.

Despair seemed a reasonable response to the onslaught launched by the parasitic diseases MSX and dermo. The diseases cannot harm humans.

Beginning in the 1960s, and accelerating in the 1980s for reasons that remain unclear, the diseases swept through the bay's oyster bars. The oyster population quickly dropped, to about 1 percent of historic levels.

Harvests plummeted. In Maryland's portion of the bay, the catch went from an average of 2.2 million bushels a year to fewer than 500,000 in the late 1980s, and then to just 80,000 bushels in the winter of 1993-94.

Last winter, the harvest during Maryland's season, which runs from October through March, jumped nearly 50 percent from the previous season, to 423,000 bushels. This year, the harvest seems to be nearly as strong, said John Surrick, a spokesman for the Maryland Department of Natural Resources.

Virginia's harvest languishes at roughly one-tenth of Maryland's, in part because the parasitic diseases thrive better in saltier water, and Virginia's part of the bay is nearer the Atlantic Ocean.

In both states, oysters for most of the past century were the leading moneymaker for commercial watermen. In a plunder that some compare to the slaughter of the carrier pigeon or the American bison, powered oyster dredges chewed through reefs that took thousands of years to form.

As the bay's health deteriorated, water-clouding sediment smothered immobile baby oysters. Algae blooms fed by pollution absorbed the oxygen oysters and other life needed to grow in good health.

Scientists think they may have found a formula for success. It calls for protecting old oysters, which simply by surviving more than several years have shown they can survive the diseases. Concentrations of disease-resistant oysters might spawn resistant offspring.

Something like that may already be occurring, said Stephen Jordan, director of the Sarbanes Cooperative Oxford Laboratory, a joint federal and state research facility on the Eastern Shore.

Last year's drought lowered freshwater flows into the bay, and salinity levels were high. That left disease levels high, too. But, Jordan said, "We didn't see the extremely high levels of mortality we would expect."

Baywide, about 34 percent of oysters had died, compared with mortality rates of 45 percent in the early 1990s.

And no place registered the 90 percent mortality levels once seen, Jordan said.

It is possible that oyster deaths were simply delayed, Jordan said. But it's also possible that oysters are becoming disease-tolerant. "We're cautiously optimistic about that," Jordan said.

So is Keen, the waterman, who lives in Dunkirk in Calvert County.

"Every day is an opportunity," said Keen, 38, as he stood, wearing drab green foul-weather gear, on the Long Shot's gently pitching deck.

Rain fell noiselessly. Three other work boats appeared at this spot, a map coordinate about a mile from Annapolis, marked by an empty oil jug Keen put out earlier as a makeshift buoy.

His day's harvest started slow, the powered tongs pulling paltry handfuls of shell from the oyster bar below.

"We'll run into a whole pile of shells shortly," Keen said. "Just gotta find it."

He did. The pace quickened. Heavy nylon rope spun noisily in and out of a pulley overhead as the tongs dropped, scooped shut on the oyster bar, and rose. They dumped heaps of shell on a steel table welded to the deck.

Keen sorted, continually, purposefully, extracting oysters that had grown to the legal minimum size of three inches. He threw back plenty that were just undersized--a good sign for seasons to come, Keen said.

A few hours into the day, the tongs pulled up an oyster four inches long. That made it old, a survivor, maybe four years old and clearly long past the age when disease tends to kill.

It was covered in mud.

"Beautiful," said Keen.

CAPTION: Waterman Kenny Keen harvests oysters about a mile off Annapolis.

CAPTION: Waterman Kenny Keen breaks oysters and mussels apart and measures the oysters while working a bar about a mile from Annapolis.

CAPTION: Keen carries part of his haul from his work boat. The Dunkirk man remembers recent years when he wouldn't waste the time or fuel taking his oyster boat out.

CAPTION: Keen uses patent tongs, a type of powered rake, to deposit his catch aboard his boat, the Long Shot. Watermen like Keen have seen the bay's oyster population rebound during the past two years.