The Treasury Department sold $6.4 billion in new three-month bills at an average discount rate of 5.80%, up from 5.12% last week. Another $6.4 billion was sold in new six-month bills at an average discount rate of 6.24%, up from 5.98% last week. The rates were the highest since Oct. 19, when three-month bills sold for 6.84% and six-month bills averaged 7.21%. The new discount rates understate the actual return to investors--5.98% for three-month bills with a $10,000 bill selling for $9,853.40 and 6.55% for six-month bills selling for $9,684.50. The discount rate reflects the price discount received when government securities are purchased at less than face value.