The Federal Reserve said the average yield for one-year Treasury bills, the most popular index for making changes in adjustable rate home mortgages, fell to 6.61% last week after averaging 6.71% the week before . . . Monoclonal Antibodies Inc. said it has learned that a complaint has been filed against it alleging securities law violations in connection with the company's public statements and SEC filings . . . Baker Hughes Inc. reported that the number of working oil and gas rigs in the United States this week totaled 891, up 19 from last week and an increase of more 200 from this time last year, when the count dropped to a record low.