How does a man studying nuclear chemistry at M.I.T. end up conducting the world's great orchestras and recording some of its most popular operas?

For Antonio de Almeida it does not seem to have been either difficult or illogical. "Science pits the intellect against the emotions," he says, "which is very exciting, but music unites them . . . and that's the greatest satisfaction I know."

Now 53, Almeida has become one of the sought-after conductors in this country and Europe both for opera and orchestra appearances. In the next few months he will finish editing the complete stage works of Offenback, 130 or more, for Belwin-Mills Publishers. Next season he will conduct his own edition of "The Tales of Hoffman," which he did recently with the Miami Opera. He is signed up with the New York City Opera for several seasons and has a substantial number of recording projects spread out over the next few years. Having conducted many of the major orchestras of this country and Europe, including the Philadelphia and Chicago, and the Berlin and Vienna Philharmonics, he will be spending more time on opera in the immediate future, giving Washington a glimpse of that side of his talent tonight when he conducts Verdi's "Attila" at Wolf Trap.

Over fruit salad and cottage cheese at the Watergate, Almeida reviewed in impeccable and unaccented English his odyssey from diplomat's son in South America to nuclear chemsity in Boston to podiums all over the world.

"I was living in Buenos Aires and two friends of mine were preparing to take the entrance examinations for M.I.T. When the exams arrived, there were three sets and they were supposed to be taken by three people. They asked me to take them and I said that was ridiculous, but I did. I have always thought that it was ironic and a little unfair that I won a scholarship while my two friends failed to make the grade."

Arrived at M.I.T., Almeida found there was no orchestra on the famous campus. "So I started one. In those days I didn't even know where to seat the players, so I told them to choose their own places, that I didn't want to dictate. As soon as the word got around that we had an orchestra going, the student conductors at New England Conservatory tried to move in on us. You know how hard it is for a student conductor to get his hands on any orchestra. But we held them off."

Finishing his studies at M.I.T. in three years, thanks to the accelerated programs of World War II, Almeida returned to Buenos Aires to tell his American mother that he wanted to become a professional musician, a career that his Portuguese father, a diplomat, had not thought right for his son. His mother suggested they take the advice of their old friend, pianist Arthur Rubinstein, who happened to be in Buenos Aires at the time.

"Rubinstein was wonderful," Almeida recalls. "For three days he spent hours playing the piano in my room, and then asking me what I thought of this and that. After a while he told my mother that I had talent and he thought I should be a musician."

For graduate studies, Almeida went on to Yale -- "I wanted to go where I could study with a great man." Yale had two.

"It was a marvelous experience to study all 32 of the Beethoven sonatas with Bruce Simonds. And then there was Paul Hindemith.

"To get into Hindemith's classes, you had to take a special examination in addition to the one you took for admission to the school. You and had to go for an interview with Hindemith. He asked me why I wanted to study with him and I told him . . . I wanted to find out what makes music work. When I explained that I had no talent as a composer, he smiled and said, 'Neither do many of the students in my class.'

"This first person who ever showed me exactly how you beat time and how you communicate with an orchestra was Leonard Bernstein at Tanglewood." Almeida by this time had learned to play, "at least for my own pleasure, the piano, cello, oboe, clarinet, horn and bassoon."

Shortly after that he was picked to conduct the Portuguese National Orchestra on a European tour, and that led to his introduction to Sir Thomas Beecham, who came to Porto as a guest conductor.

Almeida remembers Sir Thomas getting out of a DC-3 and saying, with a large smile, "I have been looking forward to conducting your orchestra. And I shall be completely deaf for the next three weeks!" Pressurized cabins were far in the future in those days.

However, four months after that meeting, Beecham invited Almeida to appear as guest with his prestigious Royal Philharmonic Orchestra in London. Stage doors have been opening ever since.