THERE are those who believe that Diego Rodr'eguez de Silva y Vel'azquez (1599-1660) was the best painter who ever lived. Even those who disagree place him high on the list of the world's greatest artists. Certainly no one was more successful at translating physical reality into sumptuous, convincingly representational images; more alert to the secrets of depicting character on canvas; or more sensitive to the use of light and color in transforming the ordinary into the extraordinary.
He was a painter's painter - one of those rare masters against whom all others are weighed.
Should anyone doubt it, a visit to the Metropolitan Museum of Art's exhibition here celebrating Vel'azquez's life and work is very much in order. Not only does it include many of the originals most Americans have seen only in reproductions; it presents his very best work (with the exception of his most famous masterpieces, ``Las Meninas'' and ``The Surrender of Breda'').
The show is a once-in-a-lifetime opportunity that couldn't have occurred without the cooperation of Madrid's Museo del Prado. For the first time in its history, the Prado lent 17 major paintings by Vel'azquez to an exhibition outside Spain. Among them are several of his greatest works, including ``The Count-Duke of Olivares on Horseback,'' ``Aesop,'' ``Queen Mariana,'' ``The Forge of Vulcan,'' and ``Prince Baltasar Carlos as a Hunter.''
As major exhibitions go, this is a small one, and yet its 38 canvases pack a wallop unmatched by any other recent blockbuster - Manet and Degas included.
Part of the impact is due to the extraordinary quality of everything on view, from the earliest painting in the exhibition, ``An Old Woman Cooking Eggs'' (made when Vel'azquez was 19), to the last, ``Philip IV,'' painted three or four years before his death.
Mostly, however, the show's power derives from the truly exceptional - one is tempted to say magical - heights of pure painting achieved in a handful of the exhibited works.
I challenge anyone to name a more breathtakingly ``alive'' and luminous painting than the 1653-54 portrait ``The Infanta Margarita,'' loaned by the Kunsthistorisches Museum in Vienna. It's a work that almost defines what painting is - or can be - in the hands of an absolute master. It stands all by itself, just as do the pivotal masterpieces of Rembrandt, Rubens, Vermeer, and a handful of others. Even the quickly dashed-off vase of flowers on the table at the left is superb. Nothing quite like it was seen in European art again until Manet, more than 200 years later.
The small, cut-down version of ``Queen Mariana,'' owned by the Metropolitan, is only marginally less fine, primarily because of its fragmentary nature.
``The Garden of the Villa Medici,'' painted during Vel'azquez's first trip to Italy (1629-30), is another miracle, as indeed are the Metropolitan's ``Juan de Pareja,'' and the surprise of the exhibition - a small ``Portrait of a Man'' owned by a New York collector. The latter may be only 19 by 17 inches in size, but it holds its own against any other portrait by Vel'azquez - or anyone else.
What comes across most strongly from beginning to end is the wholeness of Vel'azquez's vision, his frank acceptance, even enjoyment, of the world as it was.
But then, life did treat him extraordinarily well. His great talent and easy-going nature made him painter to Philip IV at age 24, and from then on things went pretty much his way. He became a favorite of the king, was assigned increasingly important functions at court, and in 1659 was named a knight of the Order of Santiago.
VEL'AZQUEZ left behind a surprisingly small number of works, roughly 100 pictures from his 40-year career. For that we have the King and the Spanish court to blame - as well as Vel'azquez's apparent willingness to let ceremonial and business duties supersede creative ones.
In 1652, the King made him chamberlain of the palace, which required him to oversee the daily operations, to supervise the sojourns of the King and the court, and to attend to all lodging, clothing, and ``appurtenances.''
In addition, he was responsible for decorations and ceremonial protocol involving the royal presence outside the palace. A heavy task, and one that left him virtually no time to paint.
And yet he did occasionally set up his easel - mostly, it would seem, by royal command - in order to produce the stunning portraits for the royal family and its dwarfs and buffoons that set his art apart from every other court painter's.
WALKING around this exhibition, one cannot help but feel that Vel'azquez was the perfect painter, that he did ``define'' the art of painting, and that only a handful of artists were his equal. But what makes him even more special is the down-to-earth nature of his work. He created beauty and meaning, but always by accepting the world around him and imbuing it with his vision and sensibility, never by avoiding, idealizing, or distorting it.
The exhibition continues at the Metropolitan Museum through Jan. 7, 1990.