Royal Shakespeareans serve a feast of Edwardian elegance; All's Well That Ends Well Comedy by William Shakespeare. Directed by Trevor Nunn

While Britain is saluting New York with various events, the Royal Shakespeare Company is saluting Broadway with a luminous production of a dark Shakespearean comedy. The revival of ''All's Well That Ends Well'' at the Martin Beck Theatre is a feast of late-Edwardian elegance and opulence. A brilliant ensemble performance exploits the comic aspects of the work - from irony and satire to broad farce - and explores its poignancies. At the same time, it untangles the web of deceits and intrigues of a plot whose ends (at least theatrically) justify their means.

The subtle undercurrents of the production staged by Trevor Nunn emerge with the brief, silent prologue. The shadowy figures of a man and a woman meet at center stage for a fleeting waltz and then separate to exit in opposite directions.

Thereafter, Mr. Nunn and his RSC actors move briskly into the tale of enduring and at length requited love. Helena is the gentlewoman of Bertram's mother, the Countess of Rossillion (Margaret Tyzack). When the medical remedies inherited from her late father enable Helena (Harriet Walter) to cure the gravely ill King of France (John Franklyn-Robbins), the King rewards her by allowing the lowly gentlewoman to select a husband from his young attendant lords. Helena chooses Bertram (Philip Franks), who chooses not to be chosen. Forced by an irate King to go through with the nuptials, Bertram heads for the wars, having set what he confidently considers impossible conditions for the consummation of the marriage.

How Helena proceeds to achieve both her connubial rights and her husband's love takes ''All's Well'' from Rossillion and Paris to the environs of Florence, where Bertram is making his military reputation. Working in the Renaissance manner from a tale by Boccaccio, Shakespeare creates a comedy of deceivers undeceived and deceptions unmasked.

As one of the least deserving heroes of Shakespearean comedy, Bertram is deceived by Helena (for his own good) and by the sponging popinjay Parolles (Stephen Moore), whose cowardice is exposed in one of the play's most uproarious low-comedy scenes. Yet in the end, with his scarves and gaudy uniforms replaced by rags, Parolles becomes a pathetic figure. His fate and the venerable Lafeu's (Robert Eddison) ironic tolerance of him express one of the comedy's underlying themes: ''The web of our life is of a mingled yarn, good and ill together. . . .''

Mr. Nunn and his associates have set forth the mingling with high artistry. It begins with the visual concept carried out by set designer John Gunter and described by Mr. Nunn (in a New York Times interview) as ''a 19th-century or early 20th-century world, a house from Chekhov's 'Seagull' in the country and a belle epoque exuberance when the action moves to Paris.'' Thus the basic setting , which resembles a large, glass-enclosed pavilion, can be transformed with incidental props and embellishments from courtly interiors to an Italian war front, a Florentine station restaurant, or a street, as the needs dictate.

However improbable the situation, the portrayals are rich and deeply human. Whatever wiles she may employ in the pursuit of her errant spouse, Miss Walter's Helena is first, last, and always moved by love for the resistant bridegroom. And by his very headstrong foolishness, Mr. Frank manages to achieve some credibility in behalf of Bertram. In fact, it is the intensity of feeling throughout the entire production that gives this ''All's Well'' its sense of consistent concern.

The spectator feels it in the loving grace of Miss Tyzack's widowed Countess of Rossillion, in the royal imprimatur of Mr. Franklyn-Robbins's King, and in the delicate ironies of Mr. Eddison's beautifully spoken Lafeu. Deirdra Morris carries off Diana's baffling last-minute explanations with mischievous charm and Geoffrey Hutchings is a resolutely low-comedy Lavache. Among the other members of a notable cast are David Lloyd Meredith (the Countess's steward), Peter Land and Simon Templeman (the Dumaine brothers), and Gillian Webb (Widow Capilet).

''All's Well That Ends Well'' runs for three hours and 20 minutes, but time seldom hangs heavy at the Martin Beck. This is another marvelous evening in the theater from RSC artistic director Nunn, whose Broadway credits include ''Nicholas Nickleby'' and ''Cats.'' According to the program credits the American settings were designed in association with John Kasarda, with costumes by Linda Fisher after original designs by Lindy Hemming and lighting by Beverly Emmons after original designs by Robert Bryan. The lovely score, with its introductory Chopin-esque piano theme, was composed and arranged by Guy Woolfenden. The dances by Geraldine Stephenson grace the occasion and at one point help propel the plot.

Hurrah for the RSC salute.