"Cycladic Art: Ancient Sculpture and Ceramics of the Aegean from the N. P. Goulandris Collection," which opens to the public Sunday at the National Gallery of Art, is an exhibition haunted by two opposing spirits - one female, one genderless. By marrying, in marble, the Goddesses and the Number, the sculptors of the Cyclades brought a modern beauty to an image old as man.

A sense of time compressed, of millenia suspended, dominates this show. These mute, harmonious idols were carved 1,500 years before the fall of Troy, and yet do not look old. They were buried in the Bronze Age, but their Brancusi-like abstraction, their musical proportions, and their ability to wring astonishing variety from rigorous convention, lends them timeless freshness.

They link, in Carter Brown's phrase, "what has been and what is." They are perhaps the oldest known works of modern art.

These 5,000-year-old statutes reflect an old continuum. Their harmonies are modern, but their subject is not new. Man has carved the nude, the calm and fertile goddess, for 30,000 years, and he still does. Even as these idols invite us to think forward to the art of our day, they force us to think backward to the dawn of modern man. Their daughters may well be the abstracted nudes of Arp, Matisse, and Modigliani, but their mothers are the fecund, wide-hipped "Venuses" of European Ice Age art.

When Cycladic art was first collected in the mid-19th century, humanity's antiquity was not yet perceived. Many still believed that Darwin was a crank - that Adam had been formed of clay one day in October in 4004 B.C. Today we take a longer view. Man makes art and always has. He was carving small stone goddesses, and using colored paints and brushes under artificial light to paint the walls of caves a thousand generations before these marble works were made.

The sculptors of the Cyclades rarely carved the male, and their cup bearers, harp players and warriors - unlike their leisured goddesses - seem busy at their work. (The same is true of actors in television ads: the calm women clad in veils who sell cars on seaside cliffs are there just because they're beautiful; but the ball players, doctors, truck drivers and experts, who sell soap and beer all seem to have jobs.)

What sets Cycladic art apart from the sculpture that preceded it, and what makes it seem so modern, is not its subject, but its style. When the sculptors of the Cyclades carved the folded arms, the hips and breasts and genitals of the female body, they brought to an old image a rigorous new order, an order based on the proportions of the Golden Section, on straight lines, squares, and arcs.

The islands of the Cyclades lie north of Crete and south of Troy in sight of one another. They are scattered in the sea like so many stepping stones between Greece and asia Minor. In Greek they are the Kyklades, from "kyklos," meaning "circle," for they appear to encircle Delos, the holy isle of Apollo.

We know little of the people who lived on these islands 5,000 years ago. We do not know their language or religion, or why they buried marble bowls and idols with some of their dead. But of one thing we are certain: They had boats, and they went to sea.

They were not the first. The people of old Greece were already mining obsidian on Melos, an island in the Cyclades, 9,000 years ago. Seafarers chart courses, tidal flows and currents. In the swinging of a boom or tiller, in the straight lines of taut halyards, are the seeds of the geometries which would lead to Euclid, and which brought measurement and order to Cycladic art.

The first Cycladic goddesses look like violins, like rarefield abstractions of the thick-thighed, thick-hipped "Venuses" of older Stone Age art. But already they seem ordered. In them one sees straight lines, circles, squares. Later they were given folded arms, slim legs, and smooth faces with large noses. Idols of both sorts are included in this show.

Their variety, in each case, is as compelling as their sameness. Their necks are thick or thin, their breasts are high or low, their chins are round or pointed; some of them are pregnant; the abdomens of others show postpartum wrinkles.

None is life-like. Each of them obeys mathematical conventions. At first those island seafarers would place into their graves unworked marble pebbles worn smooth by the sea. When, later, they began to carve and polish idols, they did so in accordance with two different sorts of beauty - the beauty of the nude and the beauty of the number. Both of these are beauties we respond to still.

Pat Getz-Preziosi, an American archeologist, has spent years examining the numbers and proportions that rule Cycladic art. Her calculations and discoveries are detailed in "Art and Culture of the Cyclades," a 616-page book recently published by the University of Chicago Press.

"For each of the figure types," she writes, "a system of proportions was adhered to - in many cases stringently. The same sets of proportions were used for large and small works alike, and significantly, they bear little resemblance to natural human ones."

The heights of nearly all Cycladic idols can be accurately divided - with arcs thrown by a compass - into three or four equal parts. The outlines of the figures, the angles of their shoulders, in almost every case, also have been carefully, mathematically determined.

The so-called Golden Section - a system of proportions based upon a rectangle five units by eight - rules Cycladic art. "In measuring more than 500 right shoulders and public angles of (Cycladic) figures," writes Getz-Preziosi, "I found that fully 95 percent could be described in terms of the two complementary angles obtained from the 5.8 rectangle."

Similar proportions just as pure and pleasing were to be used later by the architects and artists who made the buildings and the statues of Italy and Greece.

There are 166 objects in the Gallery's exhibit, all of which are owned by Nico and Dolly Goulandris. In their marble bowls and bottles, in their silver cups, bronze dagger blades, and in the herring-bones and spirals of their incised decorations, one sees mathematics rule for the first time in the history of art.

A century ago the idols of the Cyclades were frequently dismissed as "ugly" or "barbaric." The artists of our own day-by paring down their images, by eliminating frills, by hymning in their work measurement and order-have helped teach us to appreciate the melodious proportions these old images obey.

Gil Ravenel, Mark Leithauser, and the other members of the National Gallery's design team, have given to these objects a museum installation of uncommon elegance. The idols seem to float; they may be seen from all sides. The beads and jugs and daggers have been given pedestals covered with dark-colored brushed suede.

"Cycladic Art: Ancient Sculpture and Ceramics of the Aegean from the N.P. Goulandris Collection" will remain on view in the Gallery's East Building through Sept. 3. CAPTION: Picture, The marble female figurine, left, is attributed to the "master" of the Goulandris collection. It and the figure at right will be on display at the National Gallery of Art from May 20 through September 3.