Bishop Lawrence H. Welsh has temporarily stepped down as leader of the 100,000-member Roman Catholic Diocese of Spokane, Wash., after being arrested on a drunken-driving charge. The bishop left Spokane on Sunday and re-entered a “stress management and alcohol abuse” program he went to for three months in 1987, the diocese said in a statement. Welsh was arrested at 3:31 a.m. Saturday after his car was stopped, court and police records showed. Because treatment programs vary in length, it is not known when Welsh will resume his duties, a statement released by the Rev. John M. Steiner, vicar general of the diocese, said. The diocese includes 86 parishes throughout eastern Washington.