Tuba or not tuba? For 250 players last night, that was not the question, but the badge of honor, the mark of collective eccentricity. As they gathered in the Department of Commerce Auditorium to rehearse for the third annual Merry Tubachristmas, they exulted in their very difference. No one worried about frostbitten lips on the Ellipse, no one criticized the occasional muffed note that sounded like a stepped-on bullfrog. This was Tubaphoria! and they were there to blow their own horns.

"We will repeat that!" said concertmaster Harvey Phillips, the University of Indiana professor who is responsible for the tubamania. He tended toward a jolly sternness as he paced his troops through a dozen Christmas carols and hymns. With the emphatic optimism of a tour guide (he leads similar instant ensembles in different parts of the country during the holiday season), Phillips said, "I want to tell you that Tubachristmas in Washington D.C. is the best I've worked with this year!"

"It's not going to make culture history," whispered Bob Pollansch, a free-lance tuba player from Falls Church. "But it's a lot of fun." Pollansch was cradling a copy of a 1590 Serpentine, a precursor of the tuba that looks, not surprisingly, like a snake. It was one of the more unusual tubas around last night, along with some antiques dating back over 150 years. There was also one double-bell tuba, Bob Mosley's 1935 King -- "they're popular in England," he said somewhat defensively. Mosley and a half dozen other tuba enthusiasts drove up from Virginia Beach. Some players came from as far away as Greensboro, N.C., Manchester, Conn., and Kalamazoo, Mich.

Jack Perlstein, who works at WMUK in Kalamazoo, flew in to visit with old friends and fellow musicians from his days in the Army Field Band in Ft. Meade. "It's once a year when some of us try to get together and have a good time," he explained. Many of the more professional players in the instant orchestra came from the various armed forces orchestras in the Washington area.

One of them, Elliot "Ike" Evans, a 10-year veteran of the Marine Band, played in his first Tubachristmas in New York seven years ago. As Evans practiced with the civilians and amateurs -- no caste system here -- his wife recalled a bit of Army lore. In the old days, she said, the bells of the tubas pointed backward, so the army bands marched into battle in front of the troops. Then somebody with Army intelligence thought of turning the bells around, and the bands moved to the rear. Talk about a tough gig.

Evans and some of the other military players had the benefit of experience playing out in the cold -- they play funerals and inaugurals. Fourteen-year-old David Leresche of Vienna didn't seem quite so sure about going outside.

"They recommended a plastic mouthpiece in weather like this," he groaned as he sat engulfed in his instrument.

The tubas, like the players, came in all sizes. Some were tall, tapering out at the top instead of the bottom; others were compact, square; still others were delicate. Some were not made of brass, but of Fiberglas. In a society of musical outcasts (Phillips explained at the outset that these concerts are "partly for the people who don't understand us or our instruments"), the Fiberglas tubas are regarded as lightweights.

The horns came, some rusty, some with tinsel draped around their bells, some wrapped in quilts, most in their necessarily odd carrying cases that look like suitcases that have settled. When the time came to march out into the cold, they went forth loudly into that good night to play for 250 die-hard tuba fans and relatives who have braved the winds of winter. Some of the park perennials in the back of the crowd were as lit as the Christmas trees on the Ellipse, but nothing could detract from the energy of massed bodies on the Ellipse stage.

The ensemble's first selection was "Adeste Fideles" and when the audience joined in on the second chorus with "Come all ye faithful," one suspected that such a description was appropriate to both sides of the stage. The playing was occasionally ragged, but somehow right; the hour of rehearsal had been well spent.

The crowd at the Ellipse loved it, clapping along, singing where they knew the words, exulting in the warm tones and deep sonorities of the tuba choir. Some blowhards rose above the ensemble playing even though Phillips had warned "It's not how loud you play, it's how well yo play." Last night, they played well enough. Those who chose not to brave the cold can catch a replay on NBC's "Magazine" Friday night.