Has Mark Knopfler gone soft in his old age? Last year he and three British cronies put together the Notting Hillbillies. That pickup band turned out a self-named album in homage to the American South that was well-intentioned but a total snore. And now, Neck and Neck, is a cornball duet record with Chet Atkins, Nashville's Mr. Guitar. Lately Atkins has concentrated on New Age jazz and fusion, but on this collaboration producer Knopfler simply gives those styles a nod and then moves on to ''aw-shucks'' country dreck. Worst offerings: Knopfler's back-patting ''The Next Time I'm in Town'' and an excrutiating parody of ''There'll Be Some Changes Made'' in which the 66-year-old Atkins declares a taste for ''groupie girls.'' Just because Knopfler wanted to make a vanity album with his guitar hero is no excuse to foist it on the rest of us. C-

