"Now, while he is 59 years and 364 days old . . ." began National Symphony music director Mstislav Rostropovich, instructing his friend composer-conductor Leonard Bernstein to a jampacked press conference at the Kennedy Center yesterday.

Bernstein, who turns 60 today, will be honored tonight at a gala concert at Wolf Trap. On the eve of that event he reflected on his life so far and on his future.

With the characteristic acuity and the wide range of interests that have made him one of the leading artistic figures in the world, Bernstein touched on these areas:

The celebration itself: "I am so overwhelmed I can hardly speak of it. Slava, in his vodka-laden generosity, said to me a couple of years ago, 'You must celebrate your birthday in the nation's capital,' and I said, 'All right, we will do it in Washington as long as I have nothing to do with it.' And after that, I forgot about it.

"Since that I have been shanghaled into conducting at the end - how could I resist when Slava is playing together with Yehudi [Menuhin] and Andre [Previn]. The amount of love that is being poured out at a time of difficulty for me is something I simply cannot express.

Compositions in progress: "Many things [compositions] are in progress. There has been, as you may know, an interruption in my life, and therefore in my composition," he said, referring indirectly to the recent death of his wife, Felicia. "And for the next few months, I will be conducting steadily, from Jerusalem and Tel Aviv to Munich and Vienna. Then, in December, there will come a long break to compose. When something is finished, you will hear it I have a feeling it will be in the realm of opera."

"My greatest reward in hearing my work is in anticipating the next work. When I draw a double bar, a work is finished. Then it is not mine any more. I have the feeling in this ripe old age, which is beginning to hit me, that I have only begun. I hope something important is coming."

The state of American music:

"One of the most significant things about the state of music today is the amount of interest in it. Now that we have been through about 60 years of avant-grade, experimental music, I find there is such curiosity about what can happen now what combinations of old standard works and new ideas. What about the verities that inform all great music, whether Josquin or Montevedri? There was something in them that made them great that composers now feel lacking in their works.

"It has begun to change. I find in the music of young composers a return to these verities, by another route of course. You cannot write another symphony by Brahms. Composers are becoming interested in the ontological functions of music. And I think this will lead to a new kind of relationship between composers and audiences. For most of this century there has been a big windy gulf between them.

"One is always neglecting areas. You do one thing and it is at the expense of something else. I may take some time to catch up on pop music, not paying attention to the avant-garde. But you do catch up."

The general unrest in the country today, and its reflection in our music:

"That is ingrained in a pluralistic country that has developed as our has. It is a sign of growth. At a place like Tanglewood the music ranges all the way from the hardest rock to the softest pop. That is the eclecticism American music is showing today.

"It is not for me to say anything about my being helpful to young people in music, except that it is one of the things I am most proud of.

"I am very grateful for everything that has happened in my life - the trials, the failures and difficult experiences. If I had to do it all over, I would do it again."

The effects of a life lived for the past 35 years in front of flash bulbs and cameras:

"It may be that I can't answer that. Others might have to. Perhaps it has ill prepared me for a 60th birthday. But no, I do not think it has affected my work."

How he would like to be remembered:

"I am not prepared for that one." Then, after a moment: "I would like to be remembered as someone who made music for his fellow human beings. Not just as someone who made music, not how well or badly, but that I made music for my fellow human beings."

Rostropovich, in introducing Bernstein, explained why he wanted the kind of birthday celebration that will take place tonight at Wolf Trap, and be seen on public television across this country, as well as abroad via satellite:

"The genius of Bernstein does not need recognition. But my idea for this concert is not a vodka bottle or flowers. I want to make a present of his compositions. I want him to sit in a hall like a king and," turning directly to Bernstein, "hear our gift to you."