UNTHER SCHULLER happily accepted the National Symphony's commission for a double bassoon concerto because of what he calls his "natural bent to defend the underdog." Besides, it would be the first concerto ever written for this lowest-sounding of the orchestra's woodwinds. Now the work is finished, and the premiere is set for Jan. 16 with the NSO.

"One can measure the contrabassoon's standing among orchestral instruments in proportion to its close relative, the bassoon -- which is still perceived as the 'buffoon' of the orchestra," Schuller says. "The contrabassoon fares even less well than that, alas, and locker room jokes, mostly unprintable, and snide asides that the instrument's name really means 'against-the-bassoon."

"The instrument is generally stereotyped as being limited to the depiction of evil, monsters, beasts, and so forth," he adds, citing Gliere's great symphony, Ilya Mourometz, Ravel's "Ma mere I'oye," and "Salome" by Richard Strauss to prove his point. But Schuller, a former professional horn player, has already composed concertos for the double bass and the tuba, underdog instruments previously neglected by composers, so he knew what he was getting into.

One would think the composer had at least one ally in the defense of this particular underdog -- the contrabassoonist.

But in fact, when Lewis Lipnick, the National Symphony's contrabassoon specialist, first saw Schuller's completed work, he shouted, "He must be mad!"

Now, several months and uncounted practice hours later, Lipnick talks about the concerto with a mixture of admiration and fearful respect. "There is one passage I worked on for more than 110 hours. It is still dangerous to play and always will be."

Lipnick has an understandable kind of love-hate relationship with his unwieldy instrument. After all, his breath has to travel the entire length of its 17 feet before any sound emerges from its hard maple. (That is one reason why the player of the contrabassoon, like certain other wind players, must always start to play a mini-second ahead of the string players, if the entire orchestral attack is to sound precise and simultaneous.) The double bassoon's double reed, which is more than four times the width of the oboe's, can give him lots more trouble than his higher-voiced colleague's instrument hands out.

"And the contrabassoon's 17 feet are not even at the same temperature if the hall is unevenly heated, as it often is," Lipnick points out. "The top might go sharp and the bottom flat. What's more, the instrument is still in a fairly primitive state. The makers are not interested in making changes in the mechanism by which it is played because no one has demanded more of it than it will do as is."

Schuller looks to possible changes in the future, both in the way the instrument is now played, and in the attitudes of those who play it, once his concerto gets into the repertoire. "That's the way it always goes," he says, talking from the experience of a man whose music for both the double bass and the tuba was at first called unplayable, but which is now part of the standard repertoire of those instruments.

One of the biggest problems in writing for the contra, or double, bassoon is, as Schuller notes, "that 99 1/2 percent of the world's musical ears quite naturally expect a melody or theme to occur in the upper or middle range. The highest note presently attainable on the contrabassoon is the C sharp directly above middle C. Thus I faced to an unprecedented extent the unusual problem of establishing for the listener the unquestioned soloistic priority of the contrabassoon, that is, of consistently attracting the listener's ears to that lowest range of our auditory spectrum."

What does a new concerto like this one cost? The National Symphony paid Schuller $5,000 for his creative work and an added $2,500 for the cost of copying out the requisite orchestral parts.

And what is it costing Lipnick? That depends on the point of view.He has had phone calls from other contrabassoonists, one at 4 a.m., asking, "What the hell do you think you're doing!" (That kind would be from a player who thought he had a comfortable job requiring no new work and minimal practice.)

As for the unending hours spent in trying to master something no one has ever done before, that is one of the musician's particular joys. If there are danger spots in the concerto that will never be totally "secure," that is precisely what the late, great Walter Gieseking once said about a passage in Ravel's "Alborado del gracioso."

The greatest satisfaction will come on Jan. 16, 17 and 18, when, for the first time in history, the man who sits back there playing, most of the time, in the orchestral basement, will sit in a chair in front of the orchestra and play a four-movement concerto that is certain to make musical history.

Thanks to imaginative program planning by Rostropovich, that program will also include the world premiere of a concerto for flute, commissioned from Alan Hovhaness by the Discount Book and Record Shop for Jean-Pierre Rampal. With Rampal as soloist, there will be juxtaposed, as Rostropovich likes to point out with something close to glees, new concertos for the ve-y lowest of woodw&nds and almost the highest. (A concerto for piccolo is not unheard of -- Vivaldi wrote some -- but that is not quite what Rostropovich had in mind.)

Hovhaness has named his new flute concerto his Symphony No. 36 (out of 38 written so far.) He wrote it in seven weeks. Schuller took about three for the four movements of his new ground-breaker. And Lipnick is hoping for fine, even temperature all across the stage of the Kennedy Center, at least for those three nights.