The National Symphony Orchestra's inaugural concert for the 1980 Osaka Festival ended with nearly half an hour of ovations punctuated by three encores.

Musically the results were mixed but in terms of audience reaction it was a total triumph and the orchestra celebrated afterward at a party that went far into the night.

On the afternoon preceding, conductor Mstislav Rostropovich used more than half of a scehduled two-hour rehearsal clearing up details of the Brahms Piano Concerto No. 1 in D Minor, which had loomed as the major problem on the program. Then he took the rehearsal into overtime polishing te Shostakovich Fifth Symphony and going over material for some of the later concerts in the series, which will involve four completely different programs in four days.

The orchestra's triumph was based solidly on the Shostakovich, the second and concluding work on the program which received a tense, exciting interpretation from its wispy opening to the final smashing drum notes. It was a highly personalized reading, powerfully accented in nearly every bar and inspiring the whole orchestra (particularly the brass and percussion) to extraordinary efforts. The audience seemed stunned at the end. Then it broke into tumultuous applause and two little girls in kimonos came on stage with bouquets for Rostropovich and concertmaster Miran Kojian.

After the first encore, Akira Miyoshi's "Sea of the Spring," whose delicately Japanese flavor was beautifully captured by harpist Dotian Carter and flutist Toshiko Kohno, Kojian presented his bouquet to Kohno. Two more encores followed, a Paganini "Motu Perpetuo" arranged by composer-in-residence Andress Makris and "the Death of Tybalt" from Prokofiev's "Romeo and Juliet." The applause continued until Rostropovich cut it short by leaving the stage and taking the orcehstra with him.

The weak item on the program was the Brahms. Although the problems of coordination which had a plagued a preview performance last week were largely eliminated, Rostropovich often adopted slow tempos -- as he did also in the Shostakovich. But in the Shostakovich the music would greater strength as its pace slowed while in the Brahms it seemed often lethargic and its dramatic possibilities were only partially explored. Soloist Alexis Weissenberg managed to coordinate his interpreatation fairly well with that of the orchestra, but this seemed to be done partly at the cost of accepting an interpretation that was not fully his own. The performance seemed dull and listless, rather than positively bad. And it was received with more-than-polite applause, the conductor and soloist being called back to take seven bows.

At a post-concert party for the orchestra, Rostropovich was in rare form, telling jokes and radiating personality, reminding the orchestra that they were "cultural ambassadors" and telling them that they could "have a good sleep, because we have done our job real good." One of his jokes concerned a pasha and his harem, and it launched him into a personal vein.

"You know what is a pasha?" he said. "Is lke a conductor."

The he told an anti-conductor joke, which he said was a true story from the days when his father was playing in an orchestra conducted by, the composer Ippolitov-Ivanov. "They were playing [Tchaikovsky's] 'Francesa da Rimini,' and the lights went out," he said. "The orchestra was in darkness for 20 minutes, but it finished playing the music. Then the lights came on again and the musicians were so very happy, they cry and hug one another. But Ippolitov-Ivanov was over in the corner, alone and crying. 'My friends,' he said, 'you are so happy, but you forget . . . I am conducting.'"

Recalling his friend Shostakovich, he compared him to Mahler and said, "If the time has come for Mahler, the time for Shoatakovich is coming.

"If Dmitri could hear our performance tonight," Rostropovich said, "He must say, 'well done.'"

Then, turning to tympanist Fred Begun, whose work had added enormously to the power of the performance, he confessed, "I hate tympanist, but I love him. He does not just play the tympani, he has a feeling inside."

The subject of drums reminded him of war, and the possibility of atomic holocaust. "Maybe the tragic second is coming," he said, "when somebody will push a button and we must all go to another world. But until that moment comes, we must show people how beautiful is our world. We must make the world safe for beauty."