LEONARD BERNSTEIN is coming back to Washington for another Aug. 25.

Next Friday night at Wolf Trap, the country's best-known composer-conductor-pianist-teacher-author will celebrate his 60th birthday. His friends and colleagues will join the National Symphony in playing, singing and talking, while thousands of fans watch over television.

In some ways, it should be a familiar experience for Bernstein. He was here on his 39the birthday in 1957 because a new musical he had just finished opened six days earlier at the National Theater. The show was called "West Side Story," and The Washington Post prophesied unhesitatingly the day after it opened that it was pointed "in the direction of a Broadway long-run hit."

Bernstein himself had done some prophesying earlier that year. At the University of Chicago on Feb. 19, he said: "Now the conducting's over and will be over for seven months while I write another show, a rather serious and tragic musical comedy for Broadway." Six months to the day after he made that remark, "West Side Story" opened here.

A more recent birthday also found Bernstein with little but Washington on his mind. In August 1971, he was putting the final touches on the score of "Mass," with which the Kennedy Center was dedicated on Sept. 8, exactly two weeks after its composer turned 53.

An examination of Bernstein's birthdays might make you wonder if his life had not somehow been arranged horoscopically so that every Aug. 25 would find his stars at their most favorable conjunction.

It was, after all, on Sunday, Aug. 25, in 1943, that Bernstein walked out onto the porch of the hotel in the Berkshires near Tanglewood where his sister, Shirley, and his piano teacher, Helen Coates, were sitting. "Meet the new assistant conductor of the New York Philharmonic," said the young man who had turned 25 that day.

He was just back from a meeting with Artur Rodzinski, the music director of the Philharmonic. Leaning up against a haystack, Rodzinski told Bernstein that God had told him to engage the talented young fellow as his assistant.

But Bernstein was never a man to sit around waiting for the next Aug. 25. It was another Sunday that brought him his biggest break, at least up to that point in his life - Sunday, Nov. 14, when less that three months after Rodzinski hired him, the next blockbuster arrived.

That was the day Bernstein's phone rang at eight in the morning. The call was from Bruno Zirato, the manager of the Philharmonic, who said tersely, "You have to conduct this afternoon's concert!" No rehearsal, and a program to be broadcast coast-to-coast over CBS. Bruno Walter, in the midst of a guest conducting engagement had come down with a bad case of the flu.

Other than a brief visit with the ailing Walter in the latter's hotel room, Bernstein had no preparation for the afternoon program, which included the "Meistersinger" Prelude, Schumann's "Manfred" Overture, a new piece of Miklas Rosza, and "Don Quixote" by Strauss.Later that morning, Bernstein phoned to his father, who had for years opposed his son's becoming a professional musician. ("How was I to know he would turn out to be Leonard Bernstein!" his father is reported to have said years later.)

"Do you remember me telling you Friday that you would have to wait 10 years to see me conduct in Philharmonic?" the son asked the father over the phone.

"Yes."

"I made a slight miscalculation," Bernstein told him. "You are going to see me this afternoon."

From that day to this, Leonard Bernstein's life has been more and more closely woven into the fabric of this country's music. For three years he was conductor of the New York City symphony, and increasingly in demand as a guest conductor all over this country and abroad.

In 1958 he became music director of the Philharmonic he had first conducted 15 years earlier. It was the beginning of an era in the orchestra's history that brought it - in playing style technique and repertoire - squarely into the mainstream of mid-20th-century musical life. Under Bernstein's direction the Philharmonic unfolded to this country the complete repertoire of Gustav Mahler as it had not previously been presented. Ranging from Haydn and Mozart to Ligeti, Schuman and Brubeck, with special attention to Charles Ives, Bernstein made Philharmonic recordings and broadcasts household words and the subject of conversations by taxicab drivers.

His remarkable gifts as a teacher who could communicate, whether with live audiences in Carnegie and Philharmonic halls or through a TV screen became more obvious and Persuasive the more Bernstein talked. His flair for explaining to laymen some of what had seemed to them the mysteries of music, without a distortion of fact, or a touch of the cute or the ham, made Bernstein one of the most effective performers yet seen on television.

In the Philharmonic years, which after 1969 saw him leave the orchestra as music director but retain the title of Laureate Conductor, he constantly broadened his perceptions - as much in Beethoven as in Stravinsky. He became the first American to conduct opera at La Scala, making his debut there in Cherubini's "Medea," with his fellow American, Maria Callas, in the title role.

Once he had plunged into the operatic world, where his special gifts created a particular kind of excitement, performances followed in New York and Vienna in a repertoire that included "Carmen," "Der Rosenkavalier," "Tristan und Isolde," "Cavalleria Rusticana," "Falstaff" and "Fidelio." During these same years, another pattern emerged: Every major Bernstein activity became a subject for possible filming, so that his performances of the Verdi "Requiem," the Mahler Eighth Symphony, or the same composer's "Das Lied von der Erde" and other large works were captured in sight as well as sound.

But Leonard Bernstein has always been more than one artist. As he said in that 1957 University of Chicago lecture, "Half the time I cease to be a creator and switch off that magic little off-and-on switch and become a performer again."

That "magic little off-and-on switch" has been "on" at regular intervals throughout his life.As far as the public knows, which means aside from several things that are now marked "juvenilia," Bernstein the composer made his first appearance with his "Clarinet Sonata," written early in 1942. Not long after giving its first performance with David Glazer, at the Institute of Modern Art, Bernstein played it with David Oppenheim. It was heard in Washington not long afterward, when Oppenheim played it here at one of the early concerts of the Institute of Contemporary Arts. Bernstein wrote the sonata when he was 21.

Ever since then, his conducting and his composing have been like twin streams whose flow may slow down at times, as one yields primacy to the other, only to pour forth again when a new plateau is reached.

For 35 years, Bernstein the conductor has enriched the world with his extraordinary insights into the music of Carl Nielsen, Richard Strauss, Aaron Copland and hosts of other creative geniuses. In those same 35 years, Bernstein the composer have created music that has entered the standard literature of orchestras, choruses, ballets, choirs, singers and instrumental soloists.

From 1943 we have the "Seven Anniversaries" for piano - dedicated to Serge and Natalie Koussevitzky, Shirley Bernstein, Aaron Copland, Paul Bowles, William Schuman and the composer's Harvard roommate, Alfred Eisner. That same year brought out the song cycle, "I Hate Music," which Jennie Tourel sang at Tanglewood on that memorable Sunday, Aug. 25, 1943, and again the night before the lightning struck on November 14.

The very next year, while the conducting stream was reaching its first broad stage, there came the "Jeremiah," first of three symphonies; the razzle-dazzle ballet, for Ballet Theater, "Fancy Free"; and its sequel, the musical "On the Town." With these it became clear that Bernstein's music - influenced by the work of Igor Stravinsky (as what musician's was not in this country in the 1940s) and aware of the music of Copland and Hindemith - had a very special American flavor and originality.

As the list of Bernstein compositions grew longer from year to year, it divided into two major areas. There were works for the stage, like "Facsimile," "Candide," "On the Waterfront," "Trouble in Tahiti," "The Dybbuk" and "Mass"; and those for the concert hall - the symphonies, "Age of Anxiety," and "Kaddish," the "Serenade" for violin, strings and percussion, the "Chichester Psalm" and, most recently, "Songfest."

In nearly every one of these, whether in his Broadway hits, or in his large orchestral works, which include "Mass" and "Songfest," Bernstein shows clearly his concern with the state of the world in which he lives. The film "On the Waterfront," for which his music has visceral power, is about the problems of long-shoremen on the New York City docks - not very far removed from the East Side which was originally to have been the site of, and give the title to "East Side Story."

Based on poems of W. H. Auden, "The Age of Anxiety" explores the inner tensions of personal loneliness in today's society, while its successor, the "Kaddish" Symphony moves directly toward the basic dilemma Bernstein stated overwhelmingly in "Mass." When that work was new, Bernstein said, "I believe that the crisis of faith is the principal crisis of our century."

Bernstein has never hesitated to make his concerns as clear in action as he has in this music. In May 1947, he went to Israel to conduct the new Palestine Symphony in Jerusalem. The following year he returned to conduct concerts that were often played within the sound of fighting, on land that had been contested the previous day. When that orchestra, renamed the Israel Philharmonic, made its first U.S. tour, opening with a program in Constitution Hall, Bernstein shared the conducting assignments with Koussevitzky.

His historic performance of Haydn's "Mass in Time of War" was given, and subsequently recorded, in Washington Cathedral for an audience of over 15,000 who came there to share Bernstein's indignation at the inauguration of Richard Nixon, which took place the following day.

Bernstein's admirers in Washington take a special pride in the fact that three of his most significant works were first performed here: "West Side Story," "Mass" and Songfest," the last two of which were also recorded here in the Kennedy Center Concert Hall.

What the years immediately ahead have in store for Leonard Bernstein is hidden from sight. But if he is on hand for an 80th birthday, then his present plans will have brought him back to Washington often, where he intends to appear as guest conductor with the National Symphony and to make more recordings with it. What music he will create, he himself may nok know. Meanwhile, he is scheduled for a concert here on September 16 with the Israel Philharmonic.

Some times ago Bernstein said, "I am a fanatic music lover. I can't live one day without hearing music, playing it, studying it or thinking about it. And all this is quite apart from my professional role as musician: I am a fan, a committed member of the musical public." Nothing could promise more to the world's music lovers, of whom so many will be joining with the audience at Wolf Trap on Friday night in wishing the guest of honor a glorious birthday.