Robert Parris paced between his piano and his harpsichord at his Chevy Chase home, taking time from his music to explain the complexities of the life of a composer.

Even while making last-minute preparations for the world premiere of his "Symphonic Variations" by the National Symphony Orchestra last week, Parris was busy working on his next commission. While the finished score for "Variations" lay on top of the harpsichord, 45 seconds of incidental music for the Folger Theatre's production of "Macbeth" was scattered across the drafting table.

In the feast-or-famine world of the modern serious composer, most go hungry. But Parris acknowledged that he has been fortunate to receive the important commission from the National Symphony, which makes very few such requests. Still, with

major orchestral commissions netting $5,000 to $8,000, he is quick to point out that it's almost impossible to survive on income from composing. "You have to ply your trade to ply your art," Parris said.

Parris' principal "trade" for the past 25 years has been instructing students in music theory at George Washington University. And while that supports a reasonably comfortable life style, he recalls working in positions that did not support his creativity. In the late 1950s, he worked as a public school teacher.

"For a very gloomy three years, I would come home at 4 o'clock in the afternoon exhausted," he said. "It can be debilitating to teach the very rudiments to uninterested children all day and then to try to forget it immediately and find the mood that would be conducive to writing real music."

If that was dispiriting, at least it was not as bizarre as playing "piano at a strange place in New York for two or three years, a kind of operatic nightclub, where the owners fancied themselves singers," he said. "There I was up until 2 or 3 o'clock every morning, playing operatic arias for the owners: the nice lady with the voice like gravel and the whiskey tenor."

Parris observed that his fortunes are the same as composers have always faced: "Bach played the harpsichord, taught the children Latin and cleaned up after them. He even played funerals, complaining once that he wasn't making enough money because not enough people were dying."

He sees a paradox, though, in the life of today's performing composer, who tries to command respect in playing as well as writing music. "It's difficult to wear two hats," he said. "Because if enough people hear you play, and think of you as a performer first, then they don't take your composing seriously." Even so, Parris has distinguished himself in the Washington music community achieving artistic success and critical acclaim as keyboard artist and composer.

"Robert Parris is one of the most distinguished composers in Washington," said Anthony Stark, program director of Washington's Contemporary Music Forum. He is "at the stage of his career that those of us in the arts call the final blooming of creative energy."

Mstislav Rostropovich, music director of the National Symphony Orchestra, commissioned Parris' "Symphonic Variations" after he conducted an earlier work by Parris, the Concerto for Five Kettledrums. The only restriction he placed on Parris was that it be a large orchestra work of more than 20 minutes.

Rostropovich emphasized that the quality in his music sets Parris apart.

"A person who composes has to have a large musical personality," Rostropovich said. "He has to be convinced that he expresses his personality through his sound, but doesn't simply arrange a collection of beautiful sounds. When I first saw the score of 'Symphonic Variations' I recognized the imprint of his personality, the same way you can't confuse the musical personalities of Mahler and Bach."

For his part, Parris is pleased to have the composition conducted by Rostopovich. "He seems to understand my music," Parris said, recalling a rehearsal for a previous work. Parris wanted to fine-tune the piece by changing the orchestration and dynamics but found that Rostropovich already had made those corrections.

A piece of music is not finished until it's performed. Parris began work on "Symphonic Variations" in June 1986, finishing the full score a year later. But that still left the individual parts to be copied, an expensive, time-consuming effort. And even as he spoke, Parris received a phone call from a cellist in the symphony who found discrepancies in the score.

"The story goes that Mozart wrote the overture to 'The Marriage of Figaro' the night before it was performed," Parris said. "But who wrote the parts? You can't get a set of parts written in an afternoon."

Writing for the theater can be even more challenging, with strict limitations on style and timing. Jim Irwin, production manager for the Folger Theatre, said he chose Parris because of his "ability to be flexible." Irwin said that he and Michael Kahn, the director of the Folger's upcoming production of "Macbeth," heard tapes of Parris' work that "had an ominous, haunting quality that we wanted for the show." Parris' music "is just extremely well-suited because the show is a fairly dark play," Irwin said.

Beyond all the planning, writing and corrections is the performance. And for Parris, that moment makes all the work worthwhile.

"From my earliest days," said the 64-year-old composer, "just the appearance of a concert hall, let alone the appearance of a nine-foot Steinway open grand on stage, was enough to raise my blood pressure."