As a kid I never let my older brother know that I liked the Carpenters,'' says Redd Kross bassist Steve MacDonald, ''because he'd probably have made fun of me endlessly.'' Probably. But now MacDonald and his guitarist brother, Jeff, are united in shameless love for the heavy-syrup pop crafted by '70s multiplatinum siblings Richard and Karen Carpenter. And they aren't alone. Redd Kross is one of 13 alternative heavyweights including Sonic Youth, Stone Temple Pilots, The Cranberries, Cracker, and Matthew Sweet who are recording an album (due this fall on A&M) that pays tribute to the duo Richard Nixon once praised as ''young America at its very best.''
''I imagine for a lot of the groups involved, there's camp appeal,'' admits Sweet. ''But the thing I found going through [the Carpenters'] records was that there's an underlying sadness in Karen's voice that lends a depth to what would otherwise be more sappy.'' Karen's anorexia-related death in 1983, at 32, no doubt contributed to that aura of tragic kitsch. But Richard, 47, (who may sing on Sweet's country-rock version of ''Let Me Be the One'') speaks with endearing gravity about his sister's gift: ''There are just certain voices that never go out of style, like a Sinatra,'' he says, ''and Karen definitely fits into that.''