Jazz has traditionally been a primarily urban music with the aggressive rhythms, colliding harmonies and strutting solos of city life. Over the past 15 years, however, a pastoral jazz strain has emerged with the patient rhythms, unfurling harmonies and meditative solos that reflect its rural bent. This new movement hasn't simplified the challenges of jazz in any way; it simply presents those challenges in a new setting.

Pastoral jazz has its roots in the late-'60s edition of the Paul Winter Consort (the latest edition will play its "Earth Mass" at the National Shrine Nov. 19). In 1971 four members of the consort left to form their own band, Oregon, which performs at the National Building Museum on Saturday. After recording at least one album a year together, the quartet agreed on a sabbatical in 1980 to pursue individual projects.

"Oregon" (ECM 23796-1), their first group album since then, reflects the four members' sabbatical explorations but doesn't quite integrate them into an ensemble sound. As a result, several pieces have a rather spacy, flaccid quality without the tension of Oregon's best work. All the pieces are splendidly played, however, and the new elements hint at a fertile second life.

The most striking new element is guitarist Ralph Towner's fascination with synthesizers. Towner has found a way to fit electronic keyboards into his pastoral sound by understating them so much that they wash and whisper rather than buzz and pop, creating a taut tug-of-war between the immense gravity of the synthesizer and the restless scampering of the acoustic guitar.

Towner plays his Prophet 5 synthesizer on all eight numbers on "Oregon." Unfortunately the synth's approach of slowly shifting atmospherics dominates the album with no sharp, impulsive sounds as counterbalance. Paul McCandless, who has veered farther in the direction of European classical music during the sabbatical, gives "Beacon," "Beside a Brook" and "Arianna" a dreamlike, floating sound with his oboe. Collin Walcott, who joined Don Cherry and Nana Vasconcelos in the Third World trio Codona during his sabbatical, adds percussion that colors rather than structures the music.

Only two pieces pull this indulgent reverie back to earth and impose a structure that forces the foursome to challenge one another. "The Rapids" is framed by Towner's driving piano figure descending with the splashing force implied by the title. This figure compels McCandless' soprano sax and Walcott's percussion to abandon carefulness and work hard just to keep up. Bassist Glen Moore's "Impending Bloom" is the album's highlight, with Walcott knocking out a tumbling momentum on the bass drum. McCandless' meditative English horn solo is always countered by rhythmic restlessness and when the whole band coalesces around Moore's lively piano figure it jolts the music from reflection into action.

If Germany's ECM Records has long dominated the pastoral jazz field, California's Windham Hill Records has become a rapidly rising rival in just a few years. "An Evening with Windham Hill Live" (Windham Hill WH-1026) has just been released to celebrate several years of phenomenal growth capped off by a new distribution deal with A&M. Recorded live at Boston's Berklee Performance Center a year ago, the album features nine of the label's artists in assorted groupings that clearly illustrate the Windham Hill tendency to wed folk forms (with their cyclical melodies and vernacular phrasing) to jazz chord progressions.

The label's two most appealing artists, Michael Hedges and Alex de Grassi, lead off by performing sparkling solo guitar pieces. Hedges' "Rickover's Dream" (about the Navy's renegade admiral) pits a lovely folk melody against an agitated, unsettling rhythm. De Grassi, who is clearly influenced by British folk guitarists Bert Jansch and John Renbourn, combines two previously separate pieces, "Turning" and "Turning Back," into a fascinating nine-minute dialogue between his stoic arpeggios and his adventurous leads.

On "Clockwork," de Grassi gets a full ensemble sound from Darol Anger (David Grisman's fiddler), Chuck Greenberg (Shadowfax's lyriconist), bassist Michael Manring and percussionist Michael Spiro. On "Spare Change," another previously unreleased song, Hedges' guitar voices are picked up and extended by Manring and pianist Liz Story without upsetting the dramatic balance. Label founder Will Ackerman unveils a new folkish guitar piece, "Visiting," and is joined by Hedges and George Winston on "Hawk Circle." Hedges will give a solo concert at the Baltimore Museum of Art tonight, while de Grassi, Shadowfax and Story will appear in a "Windham Hill showcase" at the Wax Museum on Wednesday.

Pianist George Winston, who gives a solo concert at the Kennedy Center Concert Hall next Sunday, is Windham Hill's most popular artist by far, but he seems most guilty of the self-indulgent romanticism that the label is constantly accused of. This is apparent in his medley of John McLaughlin's "Lotus Feet" and his own "Reflections" on the live album. Winston rains down loftily celebratory piano runs without ever evoking the conflict or struggle that would warrant such triumphant music.

Shadowfax has released its second album, "Shadowdance" (Windham Hill WH-1029). This West Coast sextet manages to translate the pastoral, acoustic feel of the Windham Hill sound to electric instruments like the lyricon, synthesizer, electric bass and electric guitar, sounding like a cross between Weather Report and Oregon. The writing by reed player Chuck Greenberg and guitarist G. E. Stinson isn't up to those standards yet--it often seems overly busy and derivative--but the playing instinctively balances reflective, understated passages with more aggressive challenging phrases.