Mrs. Caroline G. Dimmock and her first husband Louis Garnier don't know it, but they've just made possible the purchase of a much-needed trompe l'oeil painting for the Corcoran Gallery of Art. "The Target" -- an oil on canvas that looks like a real wooden target pierced with bullet holes -- is "a classic fool-the-eye painting by a totally unknown 19th-century American artist named A. Kline," according to Corcoran Curator of Collections Edward J. Nygren. He still hopes for a painting by the better-known John Peto some day, but for now he's very happy to have this a 16 other new acquisitions just announced by the Corcoran.

What Mrs. Dimmock actually gave the museum, back in 1893, was a pair of Italian scenes by an obscure 19th-century Swiss paintr named Johann Jakob Frey. But since the Corcoran is now chiefly interested in building its American collections, Mrs Dimmock, along with dozens of other donors both living and dead, has pitched in to buy American paintings the Corcoran wanted but couldn't afford.

It has all happened through the miracle of deaccessioning -- a practice of selling off works of art in the collection for the purposes of buying others deemed more desirable. It is a practice sometimes abused, but here used cautiously and sensibly to enrich one of the world's greatest collections of American art -- a collection that also has real gaps and almost no acquisition funds. The new works were purchased with the $673,261 raised through the sale of 100 paintings auctioned off at Sotheby's in May 1979 -- mostly 19th-century European paintings the Corcoran hadn't shown in years. The original donors, however, have been credited on the labels that hang beside the new works. Through the miracle of modern interest rates, the fund has grown even as it was being spent.

"We needed to fill certain gaps in the collection," explained Nygren, the museum's expert on 19th-century American trompe l'oeil and still life, and have acquired both. But the most important new acquisition by far is Martin Johnson Heade's 1865 'View of Marshfield." Heade was a key 19th-century American landscape painter and a key figure in luminism. The gallery -- which otherwise has an outstanding 19th-century collection -- was missing this part of the puzzle."

Theodore Stebbins, the noted Heade authority, has gone one step further in praising the 15-by-30 inch painting featuring haystacks in an open field under a clear sky. "This couldn't have been a more timely acquisition," said Stebbins. "A great Heade did not exist [before] in Washington, city which has better and more American paintings than any other city. 'View of Marshfield,' 1865, is a 'signature' subject of Heade's. It is subtly painted and a very beautiful work . . . in wonderful condition."

The Heade, at $275,000, was the most expensive new acquisition, and that was the only price the Corcoran was willing to reveal. Next most expensive -- and important -- according to Nygen was "The Belated Kid" by William Morris Hunt, which also sold in the six-figure range. This sentimental scene, showing a young peasant girl holding a baby goat, strongly resembles the work of the French Barbizon painter Jean Francois Millet, and with good reason.

"Hunt was a Boston artist of the mid-19th century who went to France and studied in Barbizon and was an intimate of Millet," explained Nygren. "He brought the Barbizon style back to America, and the painting is important to the Corcoran because we have many French Barbizon paintings -- notably the Corots in the Rotunda. This painting makes a nice bridge."

"The other area where we had a big gap," said Nygren, "is in early 20th-century Modernist art, and we've made some very judicious purchases in that area, notably a super Max Weber, a Cubist piece from 1917 called, alternately, 'The Visit' or 'Family Reunion.'" The museum also acquired Cubist works by lesser known artists such as Maniere Dawson and John Storrs, a sculptor who showed with the Stieglitz group.

"I think we did very well," said Nygren of the deaccessioning repurchasing project, "especially since the market is going up almost daily. We've been looking for a Heade since I've been here, and since the American Luminsim show at the National Gallery, prices have increased substantially. We felt if we didn't buy it now, we might never be albe to get one."

As a result of the soaring prices, however, the Corcoran did have to settle for mostly lesser-known names. "But they all relate directly to the collection," noted Nygren. "Joshua Shaw, for example, is not a well-known name or a key figure in American art history, but he brought a certain kind of English esthetic to America before the emergence of Thomas Cole, and that aspect of history was not represented here before." Works on paper by Archibald Robertson, John Vanderlyn and William Birch English have also been added. The English watercolors -- one showing Great Falls -- were acquired from C. G. Sloan, Washington auctioneers, for what Nygren called "a very reasonable price. They surely would have cost more in New York."

Among the other highlights are a naive "Portrait of a Clergyman" dating from 1800 and attributed to Frederick Kemmelmeyer; a stiffly photographic view of "Trenton Falls near Utica, N.Y." by De Witt Clinton Boutelle and a still life by Victor Dubreuil, who, like many museums, these days, "had an obsession with money," according to Nygren. His painting, circa 1887, is called Safe Money."