Hugh Wolff, associate conductor of the National Symphony Orchestra, has received the Seaver Conducting Award, a new unsolicited grant established to help promising young American conductors "on the threshold of major international careers."

The grant -- $75,000 spread over two years -- is believed to be the largest amount ever awarded to a conductor. It is given jointly by the Seaver Institute, a private foundation based in Los Angeles, and the National Endowment for the Arts. A $75,000 grant was also announced for Kent Nagano, music director of the Berkeley Symphony and assistant conductor of the Oakland Symphony. It is expected that a similar pair of awards will be announced every two years in the future.

In its secrecy of operations and the lavishness of its grants, the Seaver Conducting Award resembles the grants of the MacArthur Foundation. "I didn't even know that this award existed until I was told I had won it," Wolff, 31, said. "It's strange to think that there were people out there in the audience, surreptitiously watching me conduct and considering me for this kind of recognition."

Financially, he said, the award is "like a handful of Van Cliburn piano competition first prizes."

The award is administered by Affiliated Artists, a nonprofit organization dedicated to promoting the careers of American performing artists, which also administers the Exxon/Arts Endowment program for young conductors (Wolff was an Exxon/Arts Endowment conductor) and the Xerox Pianists Program.

The conducting awards are the first large-scale arts involvement of the Seaver Institute, which focuses its spending on special problems and challenges in American life. Funded by the estate of the late Frank Roger Seaver, the institute has previously contributed mostly to scientific and educational programs that range from the training of academically talented students to research on alcoholism, neuro-degenerative diseases and the improvement of grain crops. In the Washington area, it has funded a program on new approaches to juvenile delinquency, administered by the National Center on Institutions and Alternatives, headquartered in Alexandria.

Wolff's $75,000 will be given in two parts. A $25,000 check will be presented to him on June 12 at the American Symphony Orchestra League Conference in San Francisco. This will have no strings attached, but he will have to give an accounting of how the money was spent. The remaining $50,000 will be put into an account on which he can draw for special projects and proposals after submitting them for approval.

"This grant will give me a chance to see some productions, concerts and rehearsals that under normal circumstances I would not be able to see at all," Wolff said. "I will be able to buy lots of scores and orchestral parts that are normally very expensive to prepare.

"The neat thing about it is that it creates a certain amount of freedom to do what you dream about, without worrying about the practicalities."

For Wolff, the next problem will be to find some free time in which he can put his windfall to creative use. "When you're booked up a year or more in advance," he said, "the idea of freeing up a lot of time for reflection and study is more easily said than done."

Wolff's contract as associate conductor of the National Symphony expires this year. His final performance in this position will be the orchestra's annual Labor Day concert on the Capitol grounds. CAPTION: Picture, Hugh Wolff . . . awarded $75,000 over two years.