Many Americans still perceive the South Seas through a web of exotic images, woven largely from Gauguin's paintings of Tahiti and old movies featuring a sarong-wrapped Dorothy Lamour.

For them -- and for most of us -- the National Gallery's newest extravaganza, "The Art of the Pacific Islands," opening today, will come as a surprise for the cornucopia of art it proffers. Whenever you know or don't know about the South Seas, one thing is made very clear: there's a lot more to oceanic art than you'll ever see in the bar at Trader Vic's.

This exhibition is the most compreshensive ever assembled on the art of Polynesia, Micronesia and Melanesia, including New Guinea. The words come from the Greek, poly [meaning many]; micros [small] and melanos [black], referring to the skin pigmentation of the inhabitants. It covers 400,000 square miles of islands formed by coral, volcanic residue and part of what was once the coast of southeast Asia.

These island groups dot an ocean which covers one-third of the earth's surface, inhabited by more than 1,000 different ethic groups. Yet, until the end of World War II, their art was little know, understood, studied or even seem outside museums of natural history.

This exhibition reveal many recently discovered styles, along with the fact that by the 18th century -- probably earlier -- the visual art of this area, despite its affinities, was one of the most stylistically diverse in the world. And all with a population that most likely never exceeded that of one modern American metropolis.

The 400 masterpieces in the National Gallert show make the point. Borrowed from 70 public and private collections from all over the world, most were gathered during the earliest periods of Western contact and exploration- -several by English explorer Captain James Cook, who gathered the very first objects from this area during his three voyages between 1768 and 1775.

Because there is no way to date these works -- most of them made of wood, bark, feathers, bone and shell -- the time when they were gathered is of primary importance. Every effort has been made to show only artistic traditions which existed before the white man came. When first observed by Cook, this was a stone-age culture with only stone and shell tools -- a miraculous fact, given the high level of craftsmanship. Like stoneage cultures elsewhere, however, they were producing extraordinary works of art, not as precious objects, but as part of their religious beliefs.

Thus, there is the fascination of discovery in the Gallery's rare and stunning array. There are carved wooden figures and masks, drums and other ceremonial implements, along with decorated weapons and painted barkcloth. There are tiny ear ornaments and necklaces made from ivory, and there are huge, wood carving like the 23-foot long crocodile from New Guinea, used in religious ceremonies. There is even a full-size house front from New Guinea.

Carved elements from canoes are a recurring theme.

"The canoe, after all, was as important to these island people as the automobile is to us," explains Metropolitan Museum of Art curator Douglas Newton, who worked with National Gallery designers Mark Leithauser and Gaillard Ravenal on the installation.

The exhibition is laid out to suggest a voyage through the island groups from east to west, beginning in Hawaii. You then travel through the other small island groups of Polynesia [including Easter Islands, New Zealand and Tahiti], past Micronesia [including the Caroline Islands], to Melanesia [including New Britain, New Ireland and the Solomons]. The journey culminates in New Guinea, richest and most varied of the oceanic islands.

This is, in fact, the opposite way the Asia-based migration actually took place. "But since this is American, and Hawaii is an American, and Hawaii is an American State, we decided to begin there," says Newton.

It also makes good visual sense because the Hawaiian section makes a spectacular beginning with the ferocious six-and-a-half-foot War God Ku, short for Kukailimoku, guarding the entrance. He is flanked by three multicolored 18th-century feather capes, once worn by chiefs of appropriate rank, which recall the vestments Matisse designed for the chapel at Vence. There is more featherwork in the Hawaiian section, including a centurion-like helmet and a fearsome mask.

From other Polynesian islands there are many sensuously carved wooden bowls, notably one from Fiji which, when turned upside down takes the form of a turtle. Another covered bowl from Fiji has a Braque-like bird as decoration, while an exquisitely carved cermonial paddle from Eastern Island looks just like a Modigliani face.Such anachronistic analogies remind us what a profound effect this art as well as African art -- had on the early Modernists. It also reminds us that we still see "primitive" art backwards, through eyes trained in Mordern art.

The exhibition proceeds past a spectacular mourning dress found by Captain Cook in the Society Islands during his second voyage. Beyond the mourning dress is the small section on Micronesia, with its highly simplified abstract designs, evident in several bowls. a canoe prow and meticulously carved shell hair ornaments.

Introducing the Melanesian section are three small cases of rare archaeological material, including pot shards and stone pounders, one with a bird motif, dating from 2,000 years ago.

There are innumerable other highlights from Melanesia, which, with New Guinea, constitutes roughly half the exhibition. An oval basketry shield inlaid with shell mosaic from the Solomon Islands is again extraordinarily modern, while a highly calligraphic woodcarving from the Hermit Islands is a rare example of Indonesian influence which looks like it came via the Celts. From New Guinea, the Largest, most prolific and colorful of these islands, comes an endless array of painted barkcloth, masks, openwork carved boards and tall spirit figures, some still brightly painted and some with skulls either of ancestors or unfortunate passersby attached.

The exhibitiob is huge, occupying the 18,000 square feet of concourse-level galleries where the diamond-studded and rather overcivilized Dresden show was installed last year. For this new show the space has been completely rearranged. More open than before, it gives viewers an opportunity to see from area into the next, suggesting the interplay of stylistic influences between island groups.

With today's opening of "The Art of the Pacific Islands," the National Gallery has now welcomed one of the least know of art's stepchildren to its bosom, and it's about time. This is, in fact, the fourth in a series of National Gallery shows designed to make exo-Eurasian art better known. It follows the unforgettable "Far North" [1973] and "African Art in Motion" [1974].

Though it may leave visitors with haunting questions, this exhibition should ultimately dispel some myths and raise some consciousness. It should also help make clear once agains that what we have so long called "primitive art" is still really art that we have simply never attempted to understand and still do not understand -- in terms of the culture that produced it.

The exhibition continues through October 14th. CAPTION: Picture 1, a wooden figure of Hawaiian War God Ku, acquired in 1846 by the Peabody Museum in Salem, Mass.;

Picture 2, a feather image from Hawaii, collected on Captain Cook's third voyage in 1778-1779. From the Museum fur Volkerkunde in Vienna.!

Picture 3, an 18th-century Society Islands gorget made of sennit, feathers, sharks teeth and dog hair. From a private collection.;

Picture 4, Dance paddle, Easter Island. From the Field Museum of Natural History, Chicigo; Map, The Islands of the Pacific By Dave Cook;

Picture 5, this 23-foot carved and painted wooden crocodile was used in religious ceremonies by the people of East sepik Province, Papua, New Guinea. From the Museum of Fine Arts in Houston.

Picture 6, a rare 19th-century Solomon Islands cermonial shield made of basketry with mother-of-pearl inlay. From the Brooklyn Museum.;

Picture7, a mourning dress of bark cloth, shell feathers and coconut shell used after the death of a chief in the Society Islands. The dress was collected in the late 18th century on Captain James Cook's second voyage. From the Bernice p. Bishop Museum in Honolulu.;

Picture 8, the small ivory female figure is from tonga and was collected by Captain Cook. From the Museum fur Volkerkunde in Vienna.