Giant Sand has a growing pile of fans including the usual posse of rock critics, as well as Lucinda Williams, Juliana Hatfield, and Victoria Williams who believe, as the latter does, that ''Howe Gelb is a wonder-filled writer of poetry and journeys of the soul and psyche.'' Gelb is the iconoclastic frontman for Giant Sand, the desert-crooner trio based in Tucson, Ariz. Since they released their first album in 1984, Sand's seemingly haphazard stew of Crazy Horse guitar and scattershot lyrical musings has stripped rock to its free-associative core, earning Gelb, bassist Joey Burns, and drummer John Convertino the tag of ''best obscure band in America.'' While there are 10 Giant Sand albums out an 11th, Glum, is due in August the group's legend has been built on off-the-cuff live shows that resemble communal acid trips more than concerts. ''The stuff is already in you somewhere,'' explains Gelb, 37, ''so you wait until the moment of impact to slip it from your lip. And if it doesn't happen, which at least half the time it doesn't, then it's at least entertaining failing.''