Lou Reed's new album, Magic and Loss, is a gripping, deeply felt work many critics have been enjoying for months. But you won't be able to hear it until January. Why? Because by then-after the hoopla over the new records by Michael Jackson, U2, Guns N' Roses, and Hammer dies down-maybe you'll be more inclined to buy it. ''The record was slated for late August,'' explains Bill Bentley, senior publicist at Warner Bros. Records. ''Lou happened to be looking at a Billboard story about all the upcoming releases for September and October and felt that this record needed more room to breathe, and find a life.'' Because CDs of Magic and Loss had already been pressed, Warner shipped several to critics- most of whom have long been in Reed's corner-to allow them time to absorb it fully. Reed's decision was astute-and not far removed from what has become standard industry practice for all but the best-selling superstars during the crowded fourth quarter of the year, when consumer shopping is heaviest. Also postponed-and thus not competing against the seasonal flood of live albums, best-of compilations, and multidisc boxed sets-are new releases by Luka Bloom (Reprise), the Ramones (Sire), and El DeBarge (Warner Bros.), among others. So don't tell record companies to sit on it-they already do.