Maxim Shostakovich mounted the podium at the Kennedy Center yesterday and began to conduct -- not, as usual, the Moscow Radio Symphony, but an American press conference. It was his first public appearance since he and his 19-year-old son Dmitri defected to the West 13 days ago in Germany.

"Both my son and I voluntarily renounce the status of Soviet citizenship," the 42-year-old conductor said in Russian. "No matter how difficult it was to leave, it would have been even more difficult for me to stay -- to witness the innocent spirit of my son being broken and brutalized as it collided with our reality."

The son of famed Soviet composer Dmitri Shostakovich sat next to his own son on the American Film Institute Theater stage, flanked by translators. He was relaxed and businesslike in the glare of the lights, explaining to some 40 reporters and a dozen TV cameras that his decision to defect had "been ripening all of my conscious life." It grew definite "during the Stalin era" when his father was persecuted for "decadent formalism" and "modernist" Western elements in his work.

"Our exodus," Shostakovich read from a prepared statement before answering questions, "is a profoundly conscious step, a sign of protest . . . my spiritual legacy from my never-to-be-forgotten father, who devoted his entire life, all his creativity, to the great humanitarian ideals of mankind."

The conductor's personal calm contrasted sharply with the florid Russian in which he described the Soviet system: "The ship of our lives, long since rudderless, has gone aground on the shores of a dismal archipelago dominated by the horrible unnatural relationship between its inhabitants -- people blinded and disoriented by the total disinformation . . . even though we had almost adjusted -- at the price of crippling our souls and scarring our hearts . . . a propitious wind has now filled the sails of fate and brought the nearly rotted wreckage of our lives onto the expanses of the world's oceans of freedom."

He said that he had "unfailingly" chosen to live in the United States because of "the attention the U.S. government pays to the rights of man." That decision was "painful and frightening" because "all those who lives have touched mine will be harshly punished."

In lighter moments the conductor sat back, crossed his legs and smoked cigarettes. Asked if he had tried to defect before, he answered, "There are no two attempts."

Halfway through the press conference, National Symphony Orchestra musical director Mstislav Rostropovich, a longtime friend of the family, joined the defectors on stage. Asked how he felt, the beaming conductor said, "Can you not see my face!"

Maxim Shostakovich provided the dramatic coda to the morning's events. As he was leaving the stage, he stopped to read a telegram he had sent yesterday morning to Soviet Ambassador Anatoliy Dobrynin: "In accordance with our decision to renounce our Soviet citizenship, we are enclosing for return to you our Soviet passports." s

A crescendo of applause rose from the audience. The First Contact

Dim figures in long gray overcoats huddling in the shadowed doorways of Dresden. Cold sweat and Pulsebeats pounding like timpani at a secret rendezvous in the fog-shrouded alleys of Prague. Muffled phone calls to a man known only as Victor in East Berlin. And then, the final heart-freezing spring to freedom across no man's land as the floodlilghts flash on and the sound of silenced pistols cuts the midnight air.

That's how most Americans, steeped in the paperback politics of John Le Carre, Len Deightonand Robert Ludlum or movies like "Casablanca," think of defection. But most of the time, a State Department veteran says, the only "cloak-and-dagger stuff" occurs in the initial hours between the time the defector leaves his previous occupation and receives asylum from police or embassy.

Shostakovich yesterday dispelled any impression of intrigue in his April 11 defection. Traveling on a multi-city tour with the Soviet Radio Symphony Orchestra, father and son completed the final performance in Nuremberg that Saturday night. Then Shostakovich said, he approached a policeman in the concert hall, "and said I would like to stay in the West. And he very kindly agreed to help." The police, he said, "made contact with the American government."

The defectors arrived in New York five days later, were met by Rostropovich -- who himself defected from the Soviet Union in 1974 -- and came to Washington on Friday, April 17. Rostropovich said that he had not been in contact with Shostakovich prior to his defection, but heard about it when he arrived at the airport from a concert in San Jaun: "I just dropped my suitcase."

The Shostakoviches traveled not so much under a cloud a secrecy as under a thick smog of bureaucratic obfuscation. At U.S. government agencies, initial inquiries about the case were met with long pauses and adroit venue-shuffling: The State Department referred questions to the Immigration and Naturalization Service, which in turn referred them back to State.

Robert German, head of the Soviet desk at State, deferred to the INS because in order to meet the "requirements of refugee processing, a person would have to be interviewed by a representative of the INS," in this case at the consular office in Frankfurt. Vern Jervis, public information officer at the INS, said, "State pretty much called the shots on this situation. When there's somebody out of the ordinary, it becomes a State Department matter, since international relations could be involved."

Only the outlines of the Shostakoviches' movement from Germany to the United States are clear. After being referred to U.S. officials, Shostakovich met with the INS to begin his processing as a refugee.

By that time, according to informed sources, word was spreading through the network of Soviet emigres and refugee support groups in Europe and America, and several operations were begun at once: The Intergovernmental Committee on Migration, a Geneva-based relief organization, began looking for the Shostakoviches; calls were placed to the Tolstoy Foundation, a private, tax-exempt charity organization for the assistance of refugees; and Rostropovich appealed directly to his friend Deputy Secretary of State William Clark .

Refugees can be admitted to the United States for a year if they meet the criteria of the Refugee Act of 1980 -- which Jervis paraphrases as "someone likely to face persecution if he returns to his own country." Refugees must have a resident sponsor to sign an "assurance" of support, and after a year's "parole," refugees can apply for permanent resident status.

Shostakoviches' sponsor is the Tolstoy Foundation. Based in New York, with 10 offices in the United States and a dozen more worldwide, it was founded in 1939 by the late Alexandra Tolstoy, daughter of Count Leo Tolstoy. The ICM provided immediate travel expenses for the pair, later to be repaid by the Tolstoy Foundation, which in turn customarily collects from the refugees themselves after it has found them work.

It is usual in Soviet refugee cases that representatives of the U.S.S.R. will visit the defector and urge him to change his mind. Shostakovich said yesterday that the confrontation had occurred on Tuesday at the State Department. "We met and they expressed their opinion, I expressed mine," he said. "We parted with a mutual understanding." A spokesman for the Soviet Embassy here said that the Soviet government had "no official statement on this case." The Western Way

While in the Soviet Union, Maxim Shostakovich apparently proved an enigma. One Soviet emigre recalls that his "public voice was always in line. eAny dissatisfaction was kept very private. You do not express such feelings even to friends."

But Solomon Volkov, author of "Testimony," the 1979 book of interviews with the late Dmitri Shostakovich, remembers Maxim Shostakovich as "a free-thinking man," which "automatically puts you in a minority position."

Shostakovich was famous in Moscow for his Western clothes and AMC Javelin car. (One American Journalist recalls that the conductor once asked him for help in getting parts.) Volkov, who says he has known Shostakovich for "many, many years," concedes that he was "surpisingly Western-oriented and wore always American clothes," but adds that such habits are common for higher-income Soviet citizens, especially those who travel abroad frequently.

It is unusual for the Soviet government to permit members of the same family (mixim Shostakovich is divorced and Dmitri is his only child; he has a married sister still in the U.S.S.R.) out of the country at the same time because it eliminates one form of potential leverage against defectors.

But Shostakovich apparently had earned considerable official trust in Moscow, where he was a popular conductor, appearing frequently with the Soviet Symphony Orchestra and on Moscow television. In 1978 he joined several other Soviet artists in sending a protest letter to President Carter urging him to release an American folk singer arrested during an antinu-clear demonstration in Minnesota.

However, a foreign tour for Shostakovich and the Moscow orchestra -- scheduled for September of 1979 -- was cancled at the last minute, possibly because of Soviet fears in the aftermath of the Bolshoi Ballet defections of that year. At the time, Shostakovich called the cancellation a "pity." He had last been in Washington in January of 1971, when he conducted the NSO. He will do some again on Memorial Day on the west lawn of the Capitol, Rostropovich announced yesterday.

Shostakovich is represented by Columbia Artists Management Inc., the New York agency that handles Rostropovich and many other celebrated musicians, and is already scheduled to play with the NSO and with the London Symphony in the fall. Silent Suffering

Shostakovich and his sone join a swelling roster of Soviet artists who have defected and found their way to the United States in recent years, among them: Rostropovich; Natalia Makarova, Rudolf Nureyev and Mikhail Baryshnikov of the Kirov Ballet; Alexander Godunov, Leonid and Valentina Koslov, and Mikhail Messerer (accompanied by his 71-year-old mother) of the Bolshoi Ballet.

But none of those names is as deeply identified with Russian culture as Shostakovich.

Dmitri Shostakovich died in August 1975 of heart disease, seven years after the ailment forced him to resign as head of the Soviet composers' union. At the age of 19, he wrote his brilliant first symphony, quickly received international recognition and began experimenting with avant-garde forms.

During his 50-year career, he was in and out of favor with Soviet officials several times. In 1936, when his opera, "Lady Macbeth of Mtensk District," was performed, Stalin was in attendance. He hated it. A few days later, Shostakovich was denounced in Pravada. In the '40s, Soviet officials charged that his works "smell strongly of the spirit of the modern bourgeois music of Europe and America." Shostakovich apologized twice to the Congress of Soviet Composers for his "bourgeois formalism" and offered to correct his future compositions. By 1949, he had regained favor, and obtained official permission to visit the United States. In 1968 he was quoted as saving, "The ideology of the enemy must not penetrate our works. Every Soviet artist must feel himself a fighter for communism."

Rostropovich said yesterday that he has been "very close" to the composer's family for four decades, and recalled playing charades with the Shostakoviches at a country house when Maxim was only 6 years old. Sergei Prokofiev, who was also there, complained about the noise.

Caught up in the excitement of the press conference, Rostropovich began speaking in Russian. Of the late composer, Rostropovich's friend and teacher, he said, "he was my life to me . . . I know how much he suffered, and this is what made him keep his mouth shut -- his love of his children."

Rostropovich said that he would "devote my life" to the Shostakoviches' future in the United States. He has already been instrumental in their arrival, arranging for lodging (the address is a "secret," Rostropovich said) and even hiring the public relations firm of Braun & Co. to manage yesterday's press conference. And Rostropovich announced yesterday that he has arranged for Shostakovich to conduct the second week of NSO concerts next September, coinciding with the 75th anniversay of Dmitri Shostakovich's birth.

The composer based his 13th Symphony on lines from the Ukrainian poet Yevgeni Yevtushenko. Maxim Shostakovich quoted the poem yesterday in speaking of his "continued love" of his former country. "As time has shown," Shostakovich said, "'forgotten they that cast the curses; remembered only those they cursed.'"