Some of the strangest--and most fascinating--Christmas music I have heard was composed for Lambert Orkis, the National Symphony's staff pianist. Orkis also has been a member of the 20th Century Consort and has built an international career as the duet partner of several of the greatest musicians of our time, notably cellist Mstislav Rostropovich and violinist Anne-Sophie Mutter.

One of his greatest claims to fame is the fact that George Crumb's "A Little Suite for Christmas" is dedicated to him. This technically brilliant, inventively descriptive work has seven recordings in circulation, a remarkable achievement for a contemporary piece of avant-garde music.

Orkis (who has made one of the recordings), gave its premiere in a program of the 20th Century Consort. Today, it is a repertory favorite at this time of year for pianists who have the powerful technique and imagination the music requires--pianists who are willing to take their instrument beyond its traditional boundaries.

One such pianist is Margaret Leng Tan, who performed Crumb's Suite and his even more complex, unorthodox and fascinating "Makrokosmos, Volume I" in a free concert Friday (repeated Saturday) at the Kennedy Center's Millennium Stage.

Tan, a native of Singapore now living in Brooklyn, has two specialties from which many other pianists would run screaming: avant-garde music that calls for extended piano techniques and music for toy piano. With these unusual interests and skills, she has built an unusual artistic profile and a spectacular, if unorthodox, career in the United States and Europe--including a compact disc, "The Art of the Toy Piano," that became a bestseller in the classical crossover category.

Her Millennium program was a birthday tribute to Crumb, who celebrated his 70th birthday in October. Crumb is one of the late 20th century's most distinctive and important American composers.

He is sometimes called a neo-impressionist, and one can detect an affinity to Debussy in his use of descriptive titles, his focus on sound-colors and his love of oblique musical allusions, but he stands essentially alone, an American original.

In the context of Crumb's work, "A Little Suite for Christmas" seems relatively sweet and simple (one might wonder whether Crumb was making a subtle pun on "suite" and "sweet"; his mind works that way.)

Compared with most other composers, the music is quite elaborate and mysterious, even with simple titles such as "The Shepherd's Noel" and "Adoration of the Magi" to help.

But "Makrokosmos" is a truly formidable work, for performers and audiences. It has 12 sections with enigmatic titles ("Primeval Sounds," "The Phantom Gondolier," "The Magic Circle of Infinity," etc.) as well as psychological and astrological overtones (each section, for example, is associated with a sign of the Zodiac).

The music rumbles, clatters, shrieks and groans; the pianist often has to reach inside and pluck the strings, making the piano sound like a harp or a drum. And, whatever this description might make you think, it is often quite beautiful. Margaret Leng Tan's performance brought out that strange beauty.

Christmas is, currently, the main business of the Millennium Stage, with the U.S. Air Force Brass Quintet performing at six this evening, Station WMAL's annual Christmas Eve program at 10 a.m. and 2 p.m. tomorrow (in the Concert Hall, not on the Millennium stage), the second annual Christmas Day Jazz Jam at 6 p.m. Saturday, the Dominion Brass on Monday, cabaret singer Judy Simmons on Tuesday and Cajun cellist Sean Grissom on Wednesday. Less clearly related to the holidays are Moonfire's program on Sunday, "Voices of Winter" next Thursday and Ron Diehl's jazz sextet on New Year's Eve--all free and all, except the WMAL show, at 6 p.m.