A ROYAL REUNION. Hans Holbein's legacy is a collection of portraits that immortalizes the court of Henry VIII. Now the king's men and women have been summoned together in an exhibition celebrating the artist with `the unfailing eye.'

It's rather touching to see Sir Henry Guildford, the formidable-looking master of the king's horse, and Mary Wotton, his rather cheekily knowing wife, together again for the first time in centuries. The German-born painter Hans Holbein the Younger took their portraits in 1527. As was his practice, he first drew them both in colored chalks and then painted his oil portraits afterward. All four works still exist. The painted portrait of Sir Henry belongs to the British royal family; that of his lady to the St. Louis Art Museum.

The drawings, too, are normally in different locations: his in the Royal Collection at Windsor, hers in the Kupferstichkabinett der "Offentlichen Kunstsammlung in Basel (the print room of the Basel Art Museum).

But now, for the first time ever, the astonishing collection of 50 Holbein portrait drawings from the Royal Collection is on exhibit (through Sept. 4) together with the even more remarkable collection of Holbein works already in Basel, the city Holbein made his home before necessity or ambition led him to seek his fortune in England. Not that this joint display pretends to be a definitive exhibition of Holbein: There are major paintings elsewhere, like his ``Portrait of Erasmus Writing'' in the Louvre, and the ``Meyer Madonna'' in Darmstadt, West Germany, as well as his masterpiece ``The Ambassadors'' in London's National Gallery.

But just bringing these two collections together provides a potent tribute to the 16th-century painter that one of his great patrons, Sir Thomas More, called ``a wonderful artist.''

It was Holbein's capacity for lifelike realism - what E.H. Gombrich has called his ``unfailing eye'' - that undoubtedly brought him contemporary fame, and made it possible for him to portray so many of the figures at Henry VIII's court. He is supposed to have portrayed more than a fifth of the English peerage. He indelibly fixed their images for posterity. In More's case, it was not just himself, but his entire family that the artist recorded (see print No. 5 on this page). The humanist scholar Erasmus (whose features are familiar to us today from Holbein's portraits, one of which is in the Basel exhibition) said More's family was ``like the academy of Plato.'' To which Kenneth Clark, in ``Civilisation,'' commented: ``They don't look oppressively intellectual, but alert, sensible people of any epoch.''

It is to Holbein, too, that the world owes its most powerful image of Henry VIII, though no firsthand drawing of the king has survived, and the mural at White Hall, in which he painted Henry standing with legs astride, was burned in the 17th century.

Today, we only know from copies and a fragment of the cartoon for the fresco what it looked like. There is a revealing half-figure portrait of Henry by Holbein in Lugano, Switzerland, but in this show, the nearest there is to a portrait of Henry is in a miniature of ``Solomon and the Queen of Sheba.'' Henry had just made himself head of the Church of England, and by casting him as Solomon, Holbein showed him as answerable only to God.

But the English collection's concentration on portraits tells only part of the story. Before he left Basel (finally in 1532), Holbein had also been variously employed - decorating the outside of houses, decorating the inside of the Council Chamber in the City Hall, and painting altarpieces and devotional pictures. His first work at Henry VIII's court had been, almost certainly at Sir Henry Guildford's instigation, as a ``decorator'' for the entertainment and ``revels,'' which were Guildford's responsibility. Like Leonardo, whom this northern painter so evidently admired, Holbein was truly a Renaissance artist. He also made illustrations and designs for books, as the exhibition bears witness.

His career as a religious artist effectively ceased when he left Basel. By then ``the arts'' in Basel, Erasmus wrote, were ``freezing.'' The city was caught up in the disturbances of the Reformation. Holbein's Roman Catholic patrons were increasingly hard pressed, and the iconoclasm that was threatening existing religious art must have discouraged its further practice.

Amazingly, many of Holbein's sacred paintings have survived, carefully treasured in Basel, so this side of his talent is by no means completely lost to us and is illustrated here. His narrative skill, and his use of effectively dramatic lighting effects, can be seen in such a mature religious work as his ``Passion Altarpiece.'' The influence of Leonardo is apparent in his ``Last Supper'' (though it is spoiled by having been cut down in size at some time). And his unremitting North European grimness in ``The Body of the Dead Christ in the Tomb'' (a grueling call to the faithful to acknowledge the divine marvel of Jesus' resurrection from the dead) shows the extremes to which he could take his realism for effect.

Basel also possesses the immeasurably sad portrait of Holbein's wife and their son and daughter, which he painted before he left them behind in Basel. Its sadness is a mystery, and has fed all kinds of speculation about Holbein's relationship with his family. But since virtually nothing is known about the personal life of this reticent artist, the causes of this deeply evoked emotion can really be understood only in terms of the expressiveness of art, rather than whatever actual human experience it was that inspired it.

Holbein was indeed a consummate artist. His style is precise, exact, linear, analytical. His portrait drawings are practical: part of the preparation process of his art. As a portraitist he was certainly objective, even with those sitters he must have known well. He gave them dignity and importance, but he convinces us that this instillation of poise was never at the expense of a true penetration to character. The very spareness with which he delineates the line of a brow, the pursing of lips, the gaze of eyes - instead of depersonalizing his subjects - seems to fix undeniably their actual presence. It's as if we'd met them. What more could portraiture do?