On March 24, 1721, Jean Sebastien Bach (using the French spelling of his name as was the court custom of that time) wrote "To His Royal Highness My Lord Christian Louis Elector of Brandenburg &c. &c. &c.

"Your Royal Highness, as I had a couple of years ago the pleasure of appearing before Your Royal Highness, by virtue of Your Highness' commands, and as I noticed then that Your Highness took some pleasure in the small talents which Heaven has given me for Music, and as in taking leave for Your Royal Highness, Your Highness deigned to honor me with the command to send Your Highness some pieces of my Composition: I have then in accordance with Your Highness' most gracious orders taken the liberty of rendering my most humble duty of Your Royal Highness with the present Concertos, which I have adapted to several instruments . . . "

And with that bowing and scraping, expected of musicians in the 18th century when they were servants of major and minor royalties, Bach dedicated to His Royal Highness Monseigneur Christian Ludwig, Margrave of Brandenburg &c. &c. &c. the six glorious concertos that alone have kept that man's name alive for over 2 1/2 centuries.

How the times have moved from the days when Leipzig accepted Bach grudgingly as the new cantor of St. Thomas' Church after they could not get either Telemann or Graupner, both of whom they much preferred. Today Bach is one of the most honored and performed composers of all time.

Within the next four weeks, the National Symphony Orchestra will present a series of eight concerts of his music in the Kennedy Center. Conducted by Karl Richter, Max Rudolf and Tamas Vasary, the concerts will include the six concertos whose imperfections Bach begged His Royal Highness not to judge with rigor. The festival will also present the four orchestral suites, written during the same years in Anhalt-Coethen that produced the Brandenburgs.

Could anything pay more eloquent tribute to the quality of the chamber ensemble that served Duke Leopold's court than these 10 magnificient works, tailored, as are so many of Bach's writings, to the varying talents of the musicians with whom he was associted?

The coming concerts also will present all eight harpsichord concertos, both concertos for violin, as well as the one for two solo violins, and the concerto for oboe and violin. The concerts of May 26 and 27 will reach into the generation of Bach musicians that followed Sebastian's in order to offer symphonies by three of his highly talented sons: Carl Phillip Emmanuel, Johann Christian and Wilhelm Friedemann.

Nothing more dramatically indicates the growth in popularity of Bach than the B Minor Mass with which the NSO concerts will close on June 10. Not so long ago this work was heard only infrequently in Washington, usually in performances by the Cathedral Choral Society. In a remarkable coincidence, that organization, under its founder Paul Callaway, will sing the B Minor this afternoon at 4 in the cathedral. No longer ago than March 24, the Oratorio Society, which will join with the National Symphony June 10, sang the mass in the Kennedy Center. Three performances of this mountain peak in less than three months is a remarkable record.

On June 23-25, the Washington Bach Competition will bring to Lisner Auditorium nearly 80 violinists and cellists vying for close to $10,000 in prizes. Only a few weeks ago, an eight-hour Bach Marathon on the organ, in Chevy Chase Presbyterian Church, drew more than five times the number anticipated by planners. The treasury of Bach cantatas is being explored by the Washington Bach Consort, formed within the past year for that very purpose, while many church choirs regularly sing them.

Clearly the year 1985 will find Washington fully prepared to mark Bach's third of the triple 300th anniversary of that incredible vintage year, the most extraordinary in the entire history of music. For it was in 1685 that Bach, Handel and Domenico Scarlatti were born: Handel on Feb 23, Bach on March 21 and Scarlatti on Oct. 26.

The National Symphony concerts, beginning Friday, point the way. The orchestra is being divided so the musicians needed for each concert will have sufficient rehearsal time. Some soloists are being brought in to join with some of the orchestra's own solo players. The latter include Sara Watkins, oboe; Miran Kojian, violin; Adel Sanchez, trumpet; and Thomas Perrazoli, flute. Gueats include Igor Kipnis, harpsichord; Edith Peinemann, violin; and Ransom Wilson, flute. In two of the programs under his direction, Karl Richter will also serve as harpsichordist.

No eight programs can more than scratch the surface of the vast Bach repertoire. Benita Valente's presence on one will make it possible to hear two of the solo cantatas. She will be joined in the B Minor Mass by contralto Maureen Forrester, tenor David Kuebler and bass Justino Diaz.

What remains untouched in these eight concerts? The Passions According to St. John and St. Matthew, the Christmas Oratorio and the motets. Then there are the more than 200 cantatas, sacred and secular, of which Albert Schweitzer wrote: "In comparison with the cantatas, everything else that Bach has done appears as hardly more than a supplement." And finally there are the incomparable keyboard works of organ and harpsichord that alone easily qualify Bach as one of the immortal giants of music; the solo sonatas and partitas for violin and cello; and such miscellaneous, unbracketable works as The Musical Offering and The Art of Fugue.