The National Gallery of Art has been given "The Invocation," a canvas it believes to be among the last completed by the dying Paul Gauguin.

It is not a masterpiece.

Its brushwork is clumsy, its colors muddy, its South Sea maidens crudely drawn. The painting is on view in Gallery 84. In those superb surroundings, among the strongly-patterned Gauguins in the Gallery's collection, the curious defects of "The Invocation" are immediately apparent. The viewer sees at once it is the weakest picture in the room.

Superior Gauguins are today worth vast sums of money. One, the "Still Life with Japanese Woodcut" of 1889, was sold last May, at auction, for $1.4 million, a record for Gauguin. Because price depends on quality, and because the tax records of those who give paintings to museums are not open for inspection, the market value of "The Invocation" is difficult to gauge.

It was given to the Gallery by John and Louise Booth of Michigan in memory of their daughter Winkie. The Booth collection is extensive and the family is wealthy. One of the Booth businesses. Booth Newspapers, Inc., was bought by S. I. Newhouse last October for $346 million.

The Booths had owned the Gauguin for more than half a century, John Booth Jr., the donrs' son, says it was acquired by his grandfather in Switzerland just after World War I. In those days pictures by Gauguin were still inexpensive, John Richardson, who appraised the work for Knoedler's before it was given to the museum, recalls that "Ralph Booth bought it for some sensationally low sum."

"The Invocation" is dated 1903, the year the painter died in an island hut on the Marquesas. His ailments were many.He suffered from syphilis and running sores. A leg that he had broken had never healed properly, and his heart was weak. He was frequently too ill to paint. "Each day some of my old strength forsakes me," he wrote a friend in France.

"A lot of late Gauguins are bad paintings," says Wayne V. Andersen, the MIT professor who has written extensively on Gauguin. "He's okay until 1902, then he starts to fall apart."

Anderson has not seen the Booth Gauguin. Nor has John Reward, who has often advised the Gallery on its post-impressionist pictures, nor Mark Roskill of Amherst, nor Theodore Reff of New York. These scholars are all recognized a authorities on Gauguin. The Gallery did not consult them before accepting the Booth gift.

"Were "The Invocation" by another painter, its authenticity might be questioned, for it seems an odd pastiche of images derived from Gauguin's early work. The central standing nude with upraised arms resembles the male figure in "Where Do We Came From? What Are We? Where Are We Going?" the large 1897 Gauguin in the Boston Museum of Fine Art. The seated figures on the left also seem drived from the Boston picture; the women on the right resemble those in another Gauguin called "L'Appel." Even the cross in the left background appears in another late Gauguin, the "Women and White Horse."

Uninventive forgers often assemble fakes from such half-familiar images, motifs from his early work in the last months of his life.

"The Invocation" is cited in Georges Wildenstein's catalogue raisonne of the pictures of Gauguin. Though the Wildenstein catalog was published in the '60s, it says the work is "lost." There is a shelf of Gaugin books in Wildenstein catalog is the only one Wildenstein catalog is the only one that cites the Booth Gauguin.

Gauguin, who was born in 1848, was a prosperous stockbroker when, in 1883, he gave himself to painting and to pursuit of the exotic. He worked as a digger on the Panama Canal, going from there to Martinique (where the climate nearly killed him). In 1891, he sailed for Tahiti. Bronzed Polynesian maidens, resembling those seen in "The Invocation," appear in many of his finest pictures.

Though he began as an impressionist, his mature work is characterized by strong and brightly - colored interlocking patterns. One of the striking oddities about "The Invocation" is how flabby its forms are.Compare its patterns, for example, with those of "Fatata Te Miti," the Chester Dale Gauguin of 1892 on display nearby.The two pictures have a similar color scheme. Both move from pinks and purples in the foregoing to a background blue and green.

The Gallery also owns other tropical Gauguins. "Words of three Devil" of 1892, a gift of the Averall Harriman Foundation, and "The Bathers" of 1898, a gift of Sam A. Lewisohn. Gauguin saw himself as part saint, part sinner, and he portrayed himself with snake and halo in the Gallery's superb self-portrait of 1889.