She is wholly free of guile, yet she stops you in your tracks. Perhaps it is her glance, half-startled and half-calm, or her partly opened mouth, or the line-dissolving light in which Vermeer has bathed her. Botticelli's Venus may be a goddess rising, Leonardo's Mona Lisa an idealized enigma. Vermeer's girl, though just a girl, is the mundane made magnificent. She is one of the chief beauties in the history of art.

Johannes Vermeer (1632-1675) was one of those Dutch masters--Rembrandt was a second, Ruisdael a third--who, 300 years ago, brought something new to painting. They made the ordinary awesome. Forty of their pictures go on public view tomorrow in a superbly scaled loan show at the National Gallery of Art.

"Mauritshuis: Dutch Painting of the Golden Age From the Royal Picture Gallery, The Hague" is grand, not grandiose. There is more pomp in its title than there is in its pictures. The painters represented thought more of Holland's cloudy skies than they did of heaven. They cared as much for peasants as they did for princes. Impatient with pretention, fond of fun and finery, they introduced to high art down-to-earth delight.

Cows go moo, harlots flirt and unembarrassed dogs go about their doggy business in these deeply humane pictures. These artists loved the crinkling of silk, the laciness of lace, a saucy joke, a good, stiff drink, baked ham, strong tobacco. They loved the real.

If Gabriel Metsu's well-dressed young Lothario has a double chin, well then he has a double chin. If kids in Delft dared to scratch graffiti on the column by the tomb of Willem the Silent, the Father of His Country, why shame on them, of course; but when Gerard Houckgeest (1600-1661) paints that martyr's monument, he shows it as it is, scratched stick figures and all. These masters won't idealize. None has more distrust for the classical conventions of ideal beauty than the mighty Rembrandt, who paints the nude Susanna, innocent and startled, rising from her bath. "It appears very extraordinary," complained Sir Joshua Reynolds, "that Rembrandt should have taken so many pains and have made at last so very ugly and ill-favored a figure." She wears jewelry at neck and wrist--and a housewife's slippers. Sir Joshua was offended by the too-tight garter which has left its impress in the sagging, sallow skin above Susanna's calf.

Many of these masters could convincingly depict the surfaces of things, the tarnish on a pewter dish, the moist gleam of an oyster shell, the sunlight on the wall. But Rembrandt had a special gift. He could peer into men's souls. Two of his self-portraits are in this exhibition, and what a pair they are.

He was 23 years old and angling for commissions when he made the first of these in 1629. The bright rivets of his armor, and his gleaming, bulbous nose are minutely painted and a young man's hope and haughtiness glow in his dark eyes. Forty years would pass before he would produce this exhibit's late self-portrait, one made the year he died. His pose is much the same, but his brushwork has grown looser. With one stroke of his brush he is able to supply the bright linen at his throat; with another he depicts the gleam of his silk turban. But his haughtiness is gone, his dark eyes have grown mild. Dr. H.R. Hoetink, writing in the catalog, describes the master's gaze as "serenely acquiescent."

The artists represented here, and the prosperous and protestant patrons whom they served, loved the textures of the real world, the fluffy gray of partridge down, the stiffness of a ruff, the translucency of porcelain. They loved oil paint as well, whether it be brushed on with brio or precision. There is a small Frans Hals, a portrait of a little boy, perhaps the painter's son, that seems to have been painted with extraordinary speed. Other artists represented--Jan Verkolje, Frans van Mieris the Elder, Pieter Codde and Abraham van Beyeren--prefer to show off brushwork that is just as tight as that of Hals is free.

Perhaps the finest landscape is Jacob van Ruisdael's huge-skyed "View of Haarlem" with its cloud-cast shadows, its windmills in the distance, and its sheets of just-bleached linen drying on green lawns. Perhaps the finest still life is by Pieter van Anraadt, a little-known provincial who painted in Deventer. It shows a glass of frothy beer, a jug, a crinkled paper containing dark tobacco, four clay pipes, a brazier. A masterwork predictive of the 19th-century paintings of America's John F. Peto, it is the only Anraadt still life that has survived.

It is astonishing to think that many of these masters were contemporaries, neighbors. They taught each other painting. Ferdinand Bol, Aert de Gelder and Carel Fabritus were among Rembrandt's students and Fabritus, in turn, may have taught Vermeer; Salomon van Ruysdael was the uncle, and probably the teacher, of Jacob van Ruisdael; Nicholaes Berchem was the the son of Pieter Claez. "The emergence around 1610 of so many painters of genius in an area of less than 60 square miles," the catalog notes, "is one of the most remarkable occurrences in the history of painting."

Though they tend to look like nearly photographic scenes from real life, many of these pictures tell moralistic stories or off-color jokes. Pieter Claesz's still life, with its skull and empty glass, ticking watch and dying candle, is a little essay on the vanity of life. Jan Steen's "The Doctor's Visit" tells a coarser story. A woman lies in bed, a doctor sits beside her. In the foreground is a chamber pot and a shoelace smouldering on a dish of coals. Arthur Wheelock, the Gallery's curator of Dutch painting, explains that still life this way: The maid is no doubt pregnant; the doctor has just dipped the shoelace in her urine and is burning it in order to diagnose her pregnancy; the painting of a rape that is seen above her bed--and the sniffing dogs in the bedroom's doorway--underscore his reading. There is much lust and laughter, and no prudery at all, in the earthy, honest pictures in this show.

They were not always loved. Vermeer's "Head of a Girl," for instance, sold for 2 guilders and 30 cents in 1882. More than half the paintings here--among them the Vermeer, the late Rembrandt self-portrait, the Hals, the Claesz, the Van Beyeren and the Anraadt--were acquired by the Mauritshuis in the present century.

By happy coincidence, that gallery, a grand house built in 1633 by Johan Maurits, a Dutch soldier and explorer, is undergoing renovation just at the time that the United States and Holland are celebrating their diplomatic bicentennial. Though a number of the best-loved paintings in the Mauritshuis--Vermeer's "View of Delft," Rembrandt's "Anatomy Lesson of Dr. Tulp" and Paulus Potter's "Young Bull"--have not made the trip, the pictures now on loan provide a splendid introduction to the art of the Dutch Masters. Their visit to this city was supported by a grant from General Telephone & Electronics. The Mauritshuis exhibit will travel to Fort Worth, Chicago and Los Angeles after closing here on Oct. 31.