After the volcano killed everybody with a sudden deadly rain of dust and pumice (fluffy little stones the size of peach pits, but deposited in an abrupt layer 20 feet deep on top of everything in the city) the little city of Pompeii lay for centuries untouched.

Everybody knew of it, of course. A famous passage in Roman literature gives an eye-witness account of the eruption of Vesuvius on Aug. 24, A.D. 79.

But it was only in 1755 that a shaft was finally sunk smack dab into the great area (a full city block) that was called, in the next two centuries, the Cattle Market. Excavation uncovered many animal bones - cows, wild boars, horses, sheep - and thus the scientific world (racing along with its usual assumptions and reasonable guesses) proclaimed it the cattle market for Pompeii.

But just at this point, in 1955, or two centuries after everybody knew it was a cattle market, along came Wilhelmina Jashemski, professor of ancient history at the University of Maryland, to begin two decades of thinking, digging, reading and asking, amid the ruined city.

Lo and behold, as a result of her work the "Cattle Market" has turned out to have been a vineyard. The bones, it is now believed, were the waste from a little eating place in the vineyard where you could buy lunch, perhaps, and have some wine.

Dr. Jashemski (her doctorate is from the University of Chicago in the unlikely field of Roman law) never meant to upset anything - not that she minds it, either - but she got deflected from law to gardening, an enviable progress.

"One day my husband (Stanley A. Jashemski, physicist with the Naval Ordance Laboratory here) said, 'The Romans loved gardens and you do, too, so why not work on them?'"

It was a marvelous idea, but it occurred to her:

"It sounded entirely too much like fun to be a serious work project."

Overcoming the Puritan view, however, she and her husband went to Pompeii in 1955 to case the joint, as you might say. She was interested in writing a book about Roman gardens and thought Pompeii would be one chapter.

At the American Academy in Rome she met, and was influenced by, Tatiana Warscher, who was teaching there.

"I suppose," she told Warscher, "the gardens to Pompeii have been done so many times, there is nothing more to add." But Warscher laughed and said:

"My dear girl, that's only picture postcard stuff."

In fact, Jashemski began to discover, hardly anything was known of the gardens. Such classical writers as Cicero, Varro, Martial, Pliny, Cato, Columella, had things to say about gardens - even Ovid forget love long enough to mention the twice-blooming roses of Paestum - but these were no guide to the gardens Jashemski was working with.

First, she got permission from the Italian authorities, who of course are in complete charge of the priceless ruins to start working there.

She found the Italians gracious beyond her expectations, and developed a fondness for the day laborers.

"One reason for our success," she said, "is that we go to the workers' homes." She was much upset once when she had to miss a laborer's wedding.

As a result, the workers feel a personal interest in the digs. One of them was proud of having the same name as a fellow running for election in Pompeii in A.D. 79. "My ancestor ran for office here," he used to say - and was undoubtedly right.

Jashemski's triumph in learning far more about Pompeii than her predecessors depended on a number of new factors: first, she is a gardener herself, and has some feel for how plants grow and are managed.

Besides, the excellent relations with the work force led them to tell her many things she could never have known. Once, seeing an unusual contour in the surface under some vines, she wondered what in the world caused the earth to be shaped in such a way.

"Why, it's fagiolini (string beans)," said Antonio, one of the workers. "It's the only crop that would have the earth done that way on Aug. 24, A.D. 79."

He took her to see a modern vegetable garden where, sure enough, the beans were still done the same way in late summer.

Another time she discovered a strange ladder in the ruins. "I could not think why it was so narrow and so tall in this garden," she said. A workman said:

"Oh, my aunt has one just like it. I've often used it. It's for picking cherries."

The trees are pruned high, and the branches are so dense that only a very narrow ladder wil get among them.

They discovered a zappa, or hoe. Just the iron blade, the wood handle having vanished.

"How long do you suppose the handle was?" she asked. "I will show you in the morning," a worker said. He brought along his own modern hoe handle, and it fit perfectly in the ancient metal blade.

One time workers were clearing weeds with martinellas - we would use machetes, but in modern Pompeii they use martinellas which are like small pick axes only with the points flattened out. You swing them.

Under a deposit of undisturbed volcano waste. Jashemski uncovered a martinella exactly like the ones they were using.

"If I had not been present myself, and known for a certainty that it was recovered beneath lapilli (pumice stones) deposited in A.D. 79. I never would have believed it was an ancient one. I would have thought a worker had dropped it in recent years."

But more than any other factor, Jashemski has had the advantage of new techniques, unknown to those who dug before. There is now a considerable minor field in the study of root structure. Thus, volcanic waste can be removed from old root cavities (the roots of course rotted and the casts made. Then these are dug up and studied. Roots of a fig or a grape or a syeamore or poplar or willow can be identified.

Another new thing is pollen analysis. You take earth and send it to the lab in London. A tremendously tedious process then begins, but ultimately you recover pollen grains, and identify them under a microscope. Thus in one garden a great amount of olive pollen was found.

"And no weed pollen. They said the gardener must have been very hard working, he had no weeds," Jashemski said.

Pliny, an authority on ancient agriculture, said grapes should be planted five feet from each other. Columella said four feet. In the "cattle yard" they followed Columella.

Jashemski was able, by careful digging, to uncover enough root cavities of grapes (and their stakes, probably of chestnut, which is still the prefered wood for stakes in modern gardens) to estimate that the "cattle yard" had in fact produced about 10,000 litres of wine a year. Sure enough, they discovered vast storage jars that would hold such a vintage.

Once, in a garden, Jashemski was deeply moved when plaster casts revealed a whole group of people trapped in the garden and suffocated by the volcanic rain. A child, a dog.

When Jashemski began, everybody believed that in the congested little city (the population is still arguable, perhaps 3,000, perhaps less) there would be no large gardens, certainly no market gardens or vineyards.

And yet within the city walls Jashemski found the large vineyard, and a large market garden. It astonished her that in ancient Pompeii they grew orchard trees, grapes and vegetables all together.

"I had assumed I would be dealing with small intimate gardens with the houses," she said. She was not prepared to find large olives, poplars (the black poplar and the white willow were used for cutting withes to tie vines to their stakes), commercial plantings of vegetables, all together, like layers in a forest.

"You'd have thought one tree would be enough in a garden," she said, "but there might instead be five large ones. Once I said I thought a piece of land was either an orchard or a vineyard or a vegetable garden, but that was before I knew they were all the same thing."

Her findings have been reported in learned publications, and she is in great demand to lecture.

"It all hits at once," she said, just back from Columbia University for a lecture, and fresh from her performance as Chancellor's Lecturer at the University of Maryland, an annual event of much prestige.

"They told me that was one lecture I should not say 'no' to," she observed.

She grew up in Eastern Nebraska, at York, where they had no forest trees, but her mother and grandfather were great gardeners, and in their house at the edge of town they had huge flower and vegetable gardens. She can still see and smell the sweet peas they has there. In Washington she had no grapes, olives, figs, but they are always fresh in her mind, which in one sense lives in Pompeii.

"Pompeii is one of the two places in the world where I always know where I am." The other place is her childhood town. Everywhere else, she is not quite sure how the streets run.

Of her work she is pleased that "it has changed our ideas" about land use in ancient cities, and pleased she discovered the first intact example of a good-sized vineyard of classical times, so that now we know how they painted and managed the grapes, how they stored and used the wine, how they worked and intercropped the land. In aid of this she is struck, not only by the sense of tragedy that is inevitable in a ruined city, but also by the continuity - today's aunts have the same ladders.

"Life," she said, "is still much the same. Did you know I have never found a garden in Pompeii that did not have a dog?"