"We're tired of these flashy museum extravaganzas with lots of gold and not much else," said Michael Kan, who has come here from the Detroit Institute of Art to help set up the tremendous pre-Columbian show at the National Gallery.

So there is only one roomful of gold things, a mere 50 objects out of the 320 that make up the first exhibition of early Costa Rican art ever seen in this country.

Brilliantly mounted by the gallery's celebrated designers Gaillard Ravenel and Mark Leithauser on the lower level of the East Building, the show is a revelation for anyone who thinks pre-Columbian art means a bunch of horrid stone skulls and square snakes. Covering three quite distinct cultures over 2,000 years, it has objects in volcanic rock and clay and jade, from a half-inch across to eight feet tall, that are sure to draw gasps for their pure, clean beauty.

Opening here tomorrow, the show, which bears the rather pompous title "Between Continents/Between Seas: Precolumbian Art of Costa Rica," leaves May 9 and will go to San Antonio (June 21 to Sept. 12), Los Angeles (Oct. 25 to Jan. 16, 1983) and later San Diego and Detroit.

Considering that scientific archeological research has come only very recently to Costa Rica, that crossroads of Central America, the sense of continuity given by this show is especially exciting. Michael Snarskis, the head archeologist at Costa Rica's Museo Nacional, noted the changes in style and point of view visible from one room to the next.

For instance, the early work from the Guanacaste-Nicoya settlements up to 500 B.C. is mostly functional pots and tools. One globular jar at the show's entrance, burnished red clay with strong vertical graffiti, is perhaps the most beautiful single creation in the whole show. Later, the art turns ceremonial and symbolic, dabbles in fantastic animals and animal-gods. The alligator appears everywhere, as does the jaguar, the largest beast in Mesoamerica. ("The spots seem to have some particular importance, we're not sure what," remarked Julie Jones, a Metropolitan Museum curator who was also here this week to preview the exhibition.) Jagged alligator fins turn up in all sorts of places.

The changes can be seen in the metates, those rectangular flat stones for pulverizing corn. Early ones are simple, functional. Gradually they take on ceremonial decorations and a concave curve like a rocker. Finally they become seats, or thrones, stunning contemporary-looking sculptures carved from brittle volcanic stone.

Stone axes, superbly crafted, give way to jade ax-god effigies, obviously never intended to be swung against a tree or a head.

A group of wildly eclectic creatures, people with antlers, animals with wraithlike sproutings where their heads should be, could have been made under hallucinogens, Snarskis said. "Those horns look like nimbuses, as though seen through a trance. Oh yes, there was a lot of drug-taking, probably ceremonial. We have incense burners and inhalers here too."

Still later, in the Central Highlands-Atlantic Watershed and especially in the Diquis area, the third and least known of the three Costa Rican cultures nestled between rain forests to the south and Mayan Mesoamerica to the north, the animal-gods seem to lose some of their magic. They are now simply people wearing animal masks. And, as the small chiefdoms become more politically sophisticated and discover the joy of war, we see statues of warriors, trophy heads and bound prisoners. Some prisoners are clearly portraits of specific individuals.

Whether from Mayan influence or not, there is evidence of human sacrifice here, in the small figures with a hole where the heart should be, in the occasional Chac-mool, that sinister supine stone god on whose flat belly human hearts were offered, and in the trophy heads, such a common decoration that sometimes they become mere bumps. Still, the overall effect is not morbid.

"The idea that the pre-Columbians were obsessed with death may be our problem, not theirs," observed Jones. "It may be something we're bringing to it in our own attitude to death. A lot depends on your world view. What seems whimsical and cute to us may have been very serious to them. They're a heavy group of folks, all right."

She was talking about the dear little clay creatures that look like spaceman dolls in their oversize helmets, and the animal-shaped whistles and ocarinas (the traditional "sweet potato" flute). Lots of ocarinas. Too many to be just toys. All tuned on a pentatonic scale. Were they for some ritual song, some chanted prayer?

Through the centuries primitive jade work develops into an intricate art with elaborate scrollwork. Suddenly, around 700 A.D., the jade production stops and gold comes in. It is handled brilliantly -- South Americans knew metallurgy 4,000 years ago, after all -- and is cast or hammered in various subtle alloys.

"They knew how to bring gold to the surface of a mixed metal by dipping it in plant acids," said Kan. "You should see the Costa Rica museum where this all came from: They have over 400 pieces."

Kan and the Detroit Institute more or less brought about the new exhibition. The institute recently sent a major selection of Old Masters to Costa Rica, which for all its high literacy rate has little chance to see the great European paintings. This exhibit returns the favor.

The mounting is inspired: Special two-faced cases have been built for the small items. The many volcanic stone articles are placed on gray sandy-surfaced pedestals that look just right. And the gold -- the wonderful miscellany of birds, alligators, cats, monkeys, deer, bats, tapirs, armadillos, lobsters, snakes and crabs -- is on a dark green suede. "We didn't want the usual red or black," said Kan, "so Gil Ravenel came up with this. We think it works."

It does, it does.