The sweltering summer of 1980 that caused crops to wither and people to suffer has had at least one happy result: the best class of baby oysters the Chesapeake Bay has seen in years.

Scientists and watermen surveying the murky bay bottom last week found large numbers of infant oysters -- commonly called "spat" -- on sand bars that have yielded none in more than a decade. They were unanimous in their opinion that the bumper baby crop comes from the water's high salt content, itself a byproduct of the dry hot summer that saw diminished freshwater flow from the rivers and little rainfall into the estuary.

"We're all encouraged by what we've seen," and Pete Jensen, Maryland's director of Tidal Fisheries, "and if nothing happens to them, in two years or so we'll have plenty of oysters to harvest."

"This year we're very optimistic," said Tony Mazzaccaro, assistant director of the University of Maryland's marine advisory program. "Guardedly so," he added."

The annual oyster crop on the bay, once 15 million bushels a year, dropped sharply around the turn of the century. oOverharvesting is generally blamed as the chief villian. In the years since, with a few exceptions, the decline has continued. The most recent baywide catch of 3.5 million bushels, however, still ranks the estuary as the world's most productive oyster area.

This year's 40th annual oyster survey, lasting eight days and covering some 200 selected "bars" where oysters grow on the bottom of the bay and its tributaries has documented a surprising story of rebirth on the ever-fragile, yet ever-tough, Chesapeake Bay.

The Aquarius, a sleek research vessel owned by the University of Maryland, began its journey of nearly 900 nautical miles from the former Potomac River resort town of Colonial Beach, Va. The Reno Hotel there recalls slot machine days when gambling casinos flourished at piers' end in Maryland waters.

Those aboard the Aquarius -- a collection of politicians, watermen and scientists -- set out in the early morning mist to gauge the whimsical force of nature.

As part of their inquirty, they sampled this year's crop of mature oysters, finding them plump and salty at the mouth of the Potomac, on the Eastern Bay and in some Eastern Shore tributaries. Along with oysters, the Aquarius dredge scooped up a few crabs in the Potomac and an empty sardine can in the Eastern Bay. But it was spat they were looking for.

And from Jones Shore on the Potomac to Bugsby Bar in the eastern bay, they found them in abundance -- baby oysters from eraser-tip size to one-inch lengths -- attached to mature oysters or empty shells planted by the state.

The spat "strike" seemed to reverse a trend. "Year by year, you could see the zeros moving farther and farther south," said Mazzaccaro of the spat counts charted at various locations each year since 1940. The baby oysters thrive in salty water, but torrents of fresh water, accompanied by silt from storms, had spoiled their natural nurseries.

Hurricane Agnes in 1972 was especially devastating. But what nature can deplete it can also replenish. The record hot summer of 1980, which turned fresh water salty, has apparently done just that.

"Look at that," said University of Maryland scientist Don Webster, pointing to a shell with eight spat. "That's what you like to see. That's the kind of stuff you like to see all over the bay."

It got better. One oyster found at the mouth of the Potomac had 51 spat clinging to it. "Isn't that beautiful?" exclaimed Elgin Dunnington of the Chesapeake Biological Laboratory at Solomons.

At each stop, a five-foot-wide dredge was hydraulically lowered into depths ranging from about seven to 25 feet. A half bushel of the catch was then dumped on a wooden culling table where several hands separated them by size and Harold Davis recorded the spat.

Davis directs Maryland's program to plant oyster shells, which attract the larvae, and to seed or move the baby oystes from nursing to growing grounds. "We have a beautiful spat set statewide on shells we planted in 1980," he beamed.

The culling crew changed with the locale, but the days were long and by Thursday one man mentioned something about overtime pay. "When we're looking for spat, it's entirely different," said Davis. Everyone laughed.

The spat set that delighted the surveyors was not universally found. There was none on samples dredged from the Potomac just below the U.S. 301 bridge. Nor did spat appear near the mouth of the Chester River on the bay's upper Eastern Shore.

"I used to oyster four or five years ago on the Wicomico River [a Potomac tributary], then the oysters got scarce. I got old and it seemed about as good a reason as any to stop," said Jim Dutton, 61, a Charles County waterman. "Maybe they'll come back there, but people my age won't see it."

"Seems like the spat are heading everywhere but the Chester River," sighed Emory (Pie) Edwards, 62, a fifth generation waterman from Rock Hall, Md., who is now a maintenance man for Kent County. "I started off handtonging oysters. That's how I'd like to end my days."

For now, oystermen from the upper Potomac and Chester Rivers can be found in their workboats in the fruitful waters of Eastern Bay, a vast inlet between Kent Island and the Eastern Shore. "At Bugsby's Bar yesterday," said Jesse J. Jump, a bearded and pony-tailed waterman from St. Michael's, "there were 25 or 30 boats from Cobb Island. That's right far from home." Cobb Island is 75 miles up the Potomac.

The survey team saw few watermen Monday on the Potomac where the spat are plentiful. The same was true for the Western Shore, where spat are in evidence for the first time in years.

Between sampling stops, they talked of conservation, production, prices and shuckers.

Dutton advocated seeding chesapeake waters with Japanese oysters, which grow to maturity in just a year. "These scientists come up with all kinds of excuses," said the waterman. "They don't want to do it."

"That's a terrible idea, absolutely awful, outrageous," said Dunnington to a reporter. "It is biologically undersirable to introduce an exotic species not adapted to this area. Second, it is very much inferior to the Eastern North American oyster. Besides, it might bring in diseases and predators our oysters may not be able to resist. If nature's not doing well, bringing in exotics is not the right answer. It's an admission of failure. It means you've done a lousy job of management."

Thursday dawned bleak and gray on the Eastern Shore. The 65-foot research boat embarked from the Kent Island narrows, headed northward at 18 knots, retraced its path through the channel and wound up at Knapp's Narrows by Tilghman Island. Clusters of workboats anchored above oyster bars known to generatioans of watermen as Shell Hill, Hollicutsnoose, Helsinki and Scotland.

At Herring Island bar, the surveyors found 34 spat per bushel, compared to 10 a year ago. At Ashcraft, they found 114, where last year they found four. At Hambleton's Hill, Harold Davis recorded 442 spat per bushel on shells planted earlier this year.

"This is our livelihood," said Bobby Hambleton, a St. Michael's waterman whose family name is immortalized by an oyster bar.

At one stop, the dredge brought up a log -- with two spat on it. At another locale, a bottle was covered with 25 baby oysters.

On Friday, the Aquarius worked the Talbot County creeks and the Tred Avon River where, apparently for the first time in recorded oyster history, some 800 spat per bushel were found. Last year there were none.

On the upper reaches of Broad Creek, the count was 3,000 spat per bushel, and it was even higher way up Harris Creek. Both had shown little or no spat a year ago.

"It was fantastic," Webster said Friday night. "We made history today."