The music has nothing to hide. It's neither friendly nor un-, and comes from places both distant and familiar.

Such are the riddlelike descriptions inspired by composer Kaija Saariaho's often-dreamy, sometimes-amorphous soundscapes, which give voice to what's felt but not seen, forces that seem to float in the ethers or rustle in the underbrush, apprehended only out of the corner of your eye and whispering in the air just a few decibels short of intelligibility.

Though in her creative prime and having won numerous prestigious awards, Finland-born Saariaho, now 55, isn't an obvious candidate for composer-in-residence status at Lincoln Center's Mostly Mozart Festival, though she inspires the audience interest to warrant such a spotlight. Virtually unknown in the United States in 2000, when the Salzburg Festival premiere of her opera L'Amour de Loin consolidated her growing reputation in Europe, Saariaho is increasingly present here now - writing new pieces for top American orchestras and seeming equally addictive to many American listeners, though those coming late to her music might need help to get up to speed with what she's writing now.

While Santa Fe Opera audiences are still contemplating Saariaho's second opera, Adriana Mater (which closes there tonight), her most abstract stage work yet, La Passion de Simone, arrives at Lincoln Center's Mostly Mozart Festival tomorrow, and repeats Friday and Sunday. It portrays the inner life of activist and writer Simone Weil (1909-43), whose mystical sense of social responsibility led her to selfless work in the French Resistance, but ended in her self-imposed starvation in England when, in an extreme act of solidarity, she refused to eat more than what she believed was allowed residents of Nazi-occupied France.

On Thursday, the City of Birmingham Symphony Orchestra performs Notes on Light - the closest Saariaho is likely to come to writing a traditional cello concerto - whose five movements have subtitles such as "Translucent, secret" or "Heart of light." The piece, which has enjoyed 18 performances in the 18 months since its premiere, is also recorded on the Ondine label for a fall release by the Orchestre de Paris under Christoph Eschenbach. On Friday, Mostly Mozart presents a late-night concert alternating between Saariaho's chamber works and those of the composer with whom she is often compared, Claude Debussy.

Debussy is one route into her world. Like his, Saariaho's music feels coloristically rich, inspired by dream states and defying the typical forces of harmonic gravity and musical logic. But their differences are more interesting. While Debussy moved in tempestuous artistic circles, Saariaho lives quietly in Paris with her husband and two children, and enjoys ongoing stage collaborations with the Lebanese poet Amin Maalouf and American director Peter Sellars. Her music contains vocal settings of spells she has gleaned from obscure civilizations. The Simone text contains aphorisms, semi-whispered: "Nothing that exists is absolutely worthy of love, so we must love what does not exist."

In person, Saariaho initially seems shy, but reveals her singular personality unguardedly: As a girl when she laid her head down to sleep, she heard music in her pillow; as a young woman, she longed to work as an organist in some remote Finnish church where she could lead a solitary, spiritual life; as an expectant mother, she heard the heartbeat of her unborn child.

With her red hair, high forehead and intense eyes, she seems fully present wherever she is, but maybe isn't there at all. She has even said that the success of L'Amour de Loin suggests to her that the piece came through her (as opposed to from her).

Musically, Saariaho isn't radical or retro, and seems not to take a definite place on that arbitrary spectrum between explosive modernists and mellifluous neotonalists. Though Debussy's innovations were reactions to centuries of Germanic evolution, Saariaho's arise from sound sources that didn't exist until recent decades: Paris' IRCAM, the electronic music-studio, created some of her early masterworks, such as the 1991 ballet score Maa, a 73-minute tour de force in the use of color and texture of electronic sound and chamber-music ensemble, starting with a travelogue of sorts that follows the sound of footsteps running through atmospheric sound landscapes.

Since then, she has emerged as perhaps the first widely known composer whose sound palette, even when created by traditional instruments, is clearly a product of the electronic age, favoring clouds of sound more than clearly articulate scales. Simone, for one, employs 32 percussion instruments that tend to glisten rather than crash and are more likely to be played by bows than by sticks. In Notes on Light, a downward glissando in the string section seems to have no end, no bottom. Her music has no floor - or ceiling.

Earlier works are clearly contained. L'Amour de Loin funneled her elusive world of sound into an extremely simple tale about a French troubadour falling in love with a far-off countess based only on her description, and dying when they finally meet. Her orchestral piece Orion, heard in 2003 at the Kimmel Center on a Cleveland Orchestra tour stop, has simple, broadly drawn motifs that feel like life rafts in an endless sea of music. That's not so much the case with Saariaho's Terra Memoria, played by the Emerson String Quartet at the Perelman Theater last fall, to be repeated at Lincoln Center Aug. 21. Or with Simone - anchored by a text, sung by soprano (Dawn Upshaw) and chorus - that looks at the tragic mystic's death from the standpoint of her grief-stricken sister.

Musically, the piece's different elements are so integrated, so superficially lustrous that listeners can easily float on the surface and never hear what's truly happening. Similarly, Notes on Light tends to be more of a continuous journey over five movements rather than something that tries to encompass an abstract idea in five different ways.

It's here that the Debussy parallels are a little disquieting. The great French composer made his name on descriptive orchestra works like La Mer though such later, more personal pieces as Jeux were neglected for decades after his death. Everything Saariaho has done thus far is so probing, so deep, you'd feel bad if the world inadvertently missed any of it. After all, she could have ended up in the Finnish wilderness, where we might never have heard of her at all.