LENOX, MASS. -- In 1940, 17-year-old Lukas Foss packed his bags and headed for the Berkshires, eager to check out a new school that offered fledgling musicians a chance to get their hands on a real orchestra.

"Everybody knew about it," recalls the composer, one of a string of distinguished alumni returning this summer to celebrate the 50th anniversary of the Boston Symphony Orchestra's training school.

"We very rarely got a chance to conduct an orchestra. At Tanglewood you would. It was something that everybody knew and everybody wanted right from the start," he said.

That 1940 season at the Tanglewood Music Center founded by the great BSO director Serge Koussevitzky glittered with the names of 20th century music: Foss and Leonard Bernstein as students, composers Aaron Copland and Paul Hindemith among the teachers.

For Foss, who has been composer in residence at Tanglewood for two years, there's an element of nostalgia to this year's celebration.

"I don't think I ever thought as a student that I would be back as the Paul Hindemith and conducting the BSO. This is very special," he said.

The 1990 season is the last of four in a celebration of Tanglewood's founding. This year's observance begins with a gala concert tonight featuring the premiere of "Celebration," an overture written by Foss for the occasion.

Seiji Ozawa, who studied at the center in 1960, will lead the BSO in a program of Stravinsky, Verdi and Puccini.

Other former students scheduled to appear this summer include Bernstein, Charles Dutoit, conductor of the Montreal Symphony Orchestra, and Zubin Mehta, conductor of the New York Philharmonic.

Some things have changed in 50 years, Foss said.

"In those days it was very different because the teacher really launched your life. They didn't call it a career either, they called it your life, your work. Nowadays they call it your career and your manager does all that," Foss said.

The shift has its good and bad sides, said Foss. Career-driven musicians are motivated to work hard, but if they come for career purposes instead of wanting to learn something, that's not so good, he said.

Recalling his days at Tanglewood, Foss said he worried Koussevitzky by signing up for classes under both the Russian-born conductor and Hindemith. But when Koussevitzky suggested Foss take a lighter load, the teenager asked for an audition to show he could handle it.

"After the audition, he said, 'If you want, you will have.' He was a wonderful, fatherlike figure to me," Foss said.

Foss said he proved a difficult pupil.

"Hindemith once wrote to Koussevitzky and said he will not teach me again because, 'Lukas wants to know but he doesn't want to follow.' Koussevitzky said, 'That's wonderful,' " Foss recalled.

The history of Tanglewood, a country estate in the Berkshire hills town of Lenox, dates back to 1937, when the BSO first began giving its popular weekend concerts. Concert-goers now pay $16 to $58 for tickets to the 4,000-seat Tanglewood Shed, a semi-open structure, or $10 to sit on the vast lawns in front of the shed.

Across the lawns is the world of the music center where a group of 100 or so Tanglewood Fellows meet in July and by the end of summer have created an orchestra of their own. At the end of this summer, the orchestra will tour Europe under Bernstein's direction.

"It's a fun place to be," Foss said. "It's not like some drudging kind of concert work, but of course the more talented the person is, the harder he works.

"Mainly, you see, what Tanglewood has, it has very wonderful people in charge. It has the right people leading it, the right people teaching and that's really the secret of its success."