IN SHIFT, U.S. OPENS EFFORT TO SETTLE TOBACCO LAWSUIT
Bush administration moves to settle Justice Department's multibillion-dollar civil lawsuit against tobacco industry, which was announced by Pres Clinton in 1999 and strongly backed by his administration; antismoking activists attack decision, while companies react with scant enthusiasm; Pres Bush has questioned suit and Atty Gen John Ashcroft opposed suit as senator and led in blocking antismoking legislation in 1998; his new effort to settle suit is based in part on belief that government might lose in trial, view gaining credence since court dismissed one portion of case last year (M)