Anyone who thought Morton Gould had retired will get a surprise Sunday when the TV series "Holocaust" opens with his 9 1/2-hour score.

At that, he'll be so busy this weekend he may not get to see the show. This is not so surprising, however, when you realize that in fact there are two Morton Goulds.

On Friday the 64-year-old composer-conductor will see the first New York performance of Eliot Feld's solo ballet, "Santa Fe Saga," written by Gould. And danced by Baryshniko. Saturday he takes the American Symphony Orchestra to West Point for a concert, repeating it the same day at Carnegie Hall. On the program: the first New York performance of the Symphony of Spirituals. By Morton Gould.

He's also working with the Cleveland Orchestra and has just finished the notes for a full-length ballet for Ballanchine, a five-year project. This in addition to his three Bicentennial commissions, which included the Symphony of Spirituals.

Quite a bit of the "Holocaust" score has been cut for the final version, but it can be heard, reorganized into a suite, on a new album. The film does not lend itself particularly to music, and much of Gould's work is "source music," background sounds integral to the story. Thus, in a scene at a Nazi dance hall, the band plays, not an actual 1940s melody but an original composition that tries to capture the essence of 1940s music.

"The timing is the hard part," Gould said, in his office at G. Schirmer Inc. "You have very precise time cues, seven-and-a-quarter seconds of this, 12 seconds of that. There are also internal cues, which make it even harder."

An internal cue is when, say after 10 of those 12 seconds, someone lifts an eyebrow on the screen and the director wants to note the change of mood.

"It's frustrating, all right. If you've got 23 seconds for a theme, you can hardly write one that takes 28 seconds. But after all, you're servicing a pictorial medium, so you can't run off on your own. Sometimes at 2 or 3 in the morning I ask myself why I'm doing this anyway.

Probably the answer is that Gould can't keep his hands off music in some form. A true prodigy, composing and playing piano at age 4, he had his first composition published when he was 6. At 8 he got a schoolarship at the Institute of Musical Art in New York, commuting from his home in Richmond Hill, L.I.

"My parents had no musical background, but they were sympathetic, and I played in concert for a few years until the Depression came along and I had to get any work I could find."

The work turned out to be vaudeville, which he came to as a pianist in the declining years. Some of the houses were in rough sections of town, and the atmosphere could be depressing, he said.

"On a Sunday matinee there'd be people lounging with their shirts off and their feet propped up on the seat in front and kids runninng up and down the aisle, and they'd just as soon throw things at you as not."

Once he and a friend played a two piano accompaniment for a dance team. The dancers made one pass across the stage and fled into the wings, leaving the pianists to face a barrage of vegetables.

"I took off, finally, but my partner wouldn't stop. They brought the curtain down and gave the cue for the next act but he still wouldn't quit, so they carried him off bodily."

At 17 Gould joined the staff of Radio City Music all, launching a career in radio, and gradually his work drew a wide audience. Like many another American composer, from Gershwin to Bernstein, whose fame rests partly on popular work, he is somewhat defensive about his serious compositions.

In "Who's Who" he takes pains to mention that his major compositions have been "played by Toscanini, Mitropolous, Monteux, Stokowski, Rodzinski, Reiner" and so on. He also lists his three symphonies, his concerto and his extensive writing for ballet and musicals from "Arms and the Girl" to the commissioned ballet, "Fall River Legend."

"Whichever side I'm working on, I'd rather be on the other side." he chuckled. "I think the abstract music, the symphonic stuff is more challenging, but you can write a two-hour symphony that's dull and a 32-bar song that has all sorts of energy and vitality. I wrote something called 'Pavane' in 1936, and if you heard it, you'd recognize it. It's been played for years; it's a standard now. At that time you weren't supposed to cross over, serious or light. But the separation isn't as rigid now. In fact, I wish I'd written a few more hits like that, now that I'mputting kids through college."

The insistence that "serious" art couldn't be popular or vice versa was a sign of America's callowness and lack of self-confidence, he thinks. In other countries, composers didn't hesitate to use pop themes and techniques, Stravinsky and Milhaud for starters.

"But we've come a long way musically," he added. "Look at the chameleon changes in pop music: swing, bop, bebop, cool jazz, soft jazz, rock . . . it's in the nature of music. They thought jazz was dead, but it came back in another form. I think we're getting more sophisticated about the whole thing."

He is also proud of the work ASCAP does - he's on its board - in helping serious musicians earn a decent living. The explosion of the record business in the last few decades has made a difference, and as a top recording artist Gould won a Grammy in 1966 for best classical record. He also writes and records a good deal of band music.

His latest project is scoring a musical based on the Fellini film, "Juliet of the Spirits."

"When you come down to it. it doesn't really matter to me whether I'm doing serious or pop. The act of writing is what I like best. the actual tactile feeling of putting notes on lined paper. Even that isn't fast enough, sometimes, when you have to put down all the notes in a chord, say. I wish they had an electronic device that would somehow give you a printout of the music direct from your brain. It's all right there."