Alberto Ginastera at 61 has the quiet, secure look of a master of world finance. But when he talks about his music, the interior creative force of the man emerges. He has been described as concealing, beneath his calm exterior, emotions with the power of a volcano. His operas have their share of murder and incest, and "Glosses," his newest work, has a finale that goes "delirant," in a delirious manner.

"I began making music on a flute with only four notes," Ginastera said, recalling his life at the age of 4. "There was no B flat, so I would play this melody, in the Argentine national anthem, like this" - playing a B natural where obviously the flat would be much better.

"One day I went into the kitchen and played on all the pots and pans and other things I could get, to make a kitchen orchestra. For this," he continued, "I was spanked. They did not know then that what I was playing had in it the roots of 'Panambi' and 'Estancia,'" he said, naming two of his early ballet successes.

Speaking in Catholic University last week, Ginastera illustrated his comments with brief excerpts from his works. Arriving at a passage from the finale of "Estancia," he said, "Always in my music there is this violent rhythm. Nature is there, sometimes calm, and sometimes with this violence."

At that point one is reminded how often, in his mature works, that rhythmic violence bursts forth. There is also in his music the strong flavor of his native Argentina.

As Ginastera began to talk about "Glosses on Themes of Pau Casals," the work of which Rostropovich gave the world premiere with the National Symphony during the past week, the composer reached back farther into his roots. "I am a man of the Mediterranean," he explained, "born in Buenos Aires. My grandparents on my father's side were Catalan, and on my mother's, Italian.

"It was Casals who told me that my name, Ginastera, is a broom-flower, a Catalan symbol. For me, 'Glosses' is a reminder of the blood-red and gold colors of the Catalan flag."

"It is also very much music for people. It has in it a feux d' artifice - a fireworks. I admire very much the 'Fireworks' of Debussy, of Stravinsky, of Rimsky-Korsakov. There is also a Sardana, a great dance in the streets, a procession which comes with great sound and then passes. Then, in the finale, fireworks."

Recalling his own growth as a musician, Ginastera said, "While I admired Debussy and Ravel and Aguirre (Julin Aguirre, a leading Argentine composer and champion of native Argentine music), I knew also that there must be another music. But in those days the music of Schoenberg had been burned in Germany, and the works of Berg and Webern were not known. So I had to find my own way. Today the young composer has everthing: serial music, atonal, electronic, music of chance."

"My international career really began here in Washington" is Ginastera's affectionate summary of his feelings for this city, in which he is enjoying world premieres in two successive weeks. Looking back over the 30 years since his first visit he recalled musicians who were of special help in launching that career.

"Harold Spivacke, the head of the music division of the Library of Congress, Howard Mitchell, the conductor of the National Symphony, and Guillermo Espinosa, the chief of the music division of the Pan American Union, these men were very important to my music. And of course Hobart Spalding, who was the head of the Opera Society, was the one who commissioned my opera, 'Bomarzo.'

"My next opera, 'Beatrix Cenci,' introduced opera to the Kennedy Center." "Cenci" opened the Opera House the second night of the Kennedy Center's career in 1971.

In Ginastera's immediate future is "Barabbas," an opera he is writing for Julius Rudel and the New York City Opera. Rudel has been the conductor of all three Ginastera operas in this country, both here and in New York, where Placido Domingo made his big debut in the first of the three, "Don Rodrigo."

Rudel is hoping to have "Barabbas" in time for a premiere a little over a year from now. In the meantime, however, for his friend, Slava Rostropovich, Ginastera is now completing yet another work which will have its premiere here next season. This week, with the composer's wife, cellist Aurora Natola-Ginastera as soloist, Rostropovich and the National Symphony will give the premiere of the Ginastera Cello Concerto in its final, revised form.

After "Barabbas," if the cellist half of the family gets her way, there will be a second cello concerto. After that, his publisher is hoping for a new piano sonata to take its place alongside the first sonata, which has been a staple of the repertoire for more than two decades.

Asked about what some are now calling a return to romantic idioms in composition, Ginastera says of his music, "I would call it not romantic, but lyric." To the students he addressed last week, he described himself as "all my life a professor, and for most of my life, a weekend composer."

As he approaches his 62nd birthday in April, Ginastera no longer teaches. From his home in Geneva, where his wife says he sometimes writes until 5 in the morning, there is flowing a stream of works in which his mature thoughts continue to find outlets in original, expressive writing.