The U.S. attorney's office has closed a 4-year-old investigation of N. W. Ayer Inc.'s handling of the U.S. Army advertising account without bringing any charges, officials of the advertising agency reported . . . The Treasury reported that Americans bought $487 million worth of U.S. Savings Bonds in October, 3% more than in September and the largest amount in three months . . . Oxnard-based Pacific Bancorp and Ventura County National Bancorp said they have agreed to merge in a stock-swap deal valued at about $15.5 million.