Raphael drawings give an inward view of the work that went into his paintings

The British have long been Raphael admirers. About a third of his known drawings are in English collections. So to celebrate the 500th anniversary of this transcendent draftsman's birth, what could be more appropriate than an exhibition bringing together for the first time all but two or three of these drawings?

The British Museum is host to ''Drawings by Raphael'' through Jan. 15. It is a wonderful exhibition, illustrating the impetus and variety of a supreme artist's development.

It would be hard to think of a more persuasive means than this show to change the minds of Raphael's doubters. It could convince them that the youngest of the three stars of the Italian high Renaissance not only had a genius for harmonious clarity and classic balance - and was a consummate assimilator and reconciler of styles - but was also a free, vigorously inventive spirit, ''always imitating, and always original,'' as 18th-century portrait painter and critic Sir Joshua Reynolds put it.

Raphael's drawings, much more than his paintings, show the passionately intuitive way in which he instilled a motif with new life, and this in spite of his almost totally utilitarian use of drawing as a means to an end. An example would be ''Virgin and Child.''

Drawings in this exhibition provide firsthand evidence of his encounter with work of Leonardo and Michelangelo in Florence. He arrived there from Umbria in 1504 at the time Michelangelo's ''David'' was erected in the Piazza della Signoria, and three drawings here attest to his absorption, and transformation, of the qualities of that statue. Another drawing, the only female nude of these formative years, is a copy (from the royal collection) of a Leonardo drawing of ''Leda and the Swan.''

He carried all his influences - including the antiquities he much admired when he was later called to Rome - on his own more than capable shoulders. But he made them subserve the direction and purpose of his own rapidly enlarging vision.

Of course, not all the drawings included are of equal interest (except perhaps to specialists). There are those made as composition studies, for instance, for the large paintings commissioned by Popes to decorate rooms in the Vatican. But every single one, nevertheless, adds something to the overall picture of his inspiration and working methods.

Few artists have been as deliberate or exhaustive. He was consistently thorough and methodical, aiming for lucidity and balance - and the concentration on essentials for which his finished works have been valued ever since.

Certainly part of the enjoyment of any fine painter's drawings is what they reveal of his thought processes. Raphael's thoroughness makes his particularly interesting in this respect. They also give a feeling of closeness to his ''autograph,'' the undisguised working of his hand. In his paintings such personal qualities tend to be smoothed away.

But some of his drawings do have the sort of completeness that makes them seem ''finished.'' There are many fine examples in this show.

These drawings still played a role in the perfecting of the final painting. They are not independent ''presentation drawings'' like some of Michelangelo's. A number are known as ''auxiliary cartoons'' - drawings that take specific details, usually heads, in the last stages before a painting is actually painted and give a final definition and attention to form, outline, light, and shade.

Other drawings of similar completeness are described as ''finished studies.''

An example is the late-Roman-period red chalk study of ''The Three Graces.'' In the show's stimulating catalog, the organizers of the exhibition, J. A. Gere and Nicholas Turner, firmly maintain that this exquisite drawing is by Raphael, in spite of modern ideas to the contrary.

The catalog, in fact, is filled with reassessments and fresh insights, particularly regarding disputed work from the beginning and end of the artist's career. The reinstatement of quite a number of drawings is proposed.

One of the fascinations of this show is its juxtaposition of works that cannot usually be seen together. Now, for a while, they are as close to each other again as when Raphael made them.

The supreme confidence of Raphael's draftsmanship, its fluent precision and amalgamation of full modeling and telling outline, triumphantly recurs throughout the exhibition, whether he is seen working in chalk, metal-point ink, or brush - and whether he is generating, planning, or finalizing. Such supreme qualities are only made more apparent in contrast with a number of drawings by members of his ''school,'' chiefly his assistants, Giulio Romano and G.F. Penni.

In an exhibition as comprehensive as this, there are bound to be some out-of-the-ordinary works.

Raphael's only measured drawing, after the antique of a rearing horse, is here. His only known drawing in the Venetian technique of black chalk on blue paper shows him exploiting an unfamiliar medium to great advantage, producing one of his most sensitive and gentle renderings of the ''Virgin and Child.''

There are drawings displaying his scrupulous preparation of work specifically for the engraver. There are two unusually ''domestic,'' genrelike drawings of clothed children with their mothers. Carefully completed, with white highlighting, these suggest a side to Raphael outside any overtly religious context.

There are several portraits. Three placed near each other are a head of Julius II, which is a ''puzzle'' to the organizers, who do not believe it to be a Raphael; a colored-chalk portrait of ''An Ecclesiast,'' traditionally by him, but only very recently seriously thought once more to be so; and a small oil portrait of Valerio Belli, one of only two paintings in the show.

The other painting is the enchanting ''Knight's Dream'' from the National Gallery here. The drawing used as the cartoon for this small picture is from the same collection. Seen together, the two are particularly intriguing. And then, talking of knights, also on view is a drawing of ''St. George and the Dragon'' that was ''hitherto unknown.'' It is in a ''private collection,'' just one more item in the wealth of drawings in Britain by the prodigious Raffaello Santi da Urbino.