With a few notable exceptions, Mexico's classical tradition is largely ignored north of the border. We may have heard of old stalwarts like Carlos Chavez, but how about Javier Alvarez and Gabriela Ortiz? They're among the best and brightest of under-40 Mexican-born composers; typical of their peers, both went to Europe for further training. The 38-year-old Alvarez has lived and taught in London since the early 80s; Ortiz, who's 30, is studying for her doctorate in electroacoustic music at London's City University. Northwestern's Jay Alan Yim, who recently won a young composer's commission from the Chicago Symphony Orchestra, heard their music last summer at the Darmstadt Festival in Germany and scheduled a sampler as part of Northwestern's newly consolidated contemporary-music series. Of the pieces on the program I'm acquainted with, Alvarez's are more inventive and unabashedly "nationalistic." His "Mambo a la Braque" (1990) from the Saydisc CD Paplotl: Transformaciones exoticas, for example, is true to its title: a bouncy cubist collage in which the well-known mambo "Caballo negro" is imaginatively deconstructed. Ortiz, on the other hand, juxtaposes a wider variety of sounds; in the structurally amorphous Things Like That Happen for cello and tape, the cello's plaintive voice asserts itself intermittently in a sea of eerie, brutal prerecorded industrial sounds. Also on the program is Antonio Fernandez Ros's Aritmetica del sol for bongos and tape. The lone performer is Ricardo Gallardo, a first-rate percussionist--also a Mexico City native now based in London--for whom Alvarez and Ortiz have written concertos. Ortiz will be present to discuss her work. Tuesday, 7:30 PM, Pick-Staiger Concert Hall, Northwestern University, 1977 South Campus Dr., Evanston; 708-491-5441 or 708-467-4000.