The Treasury Department sold $7 billion in new three-month bills at an average discount rate of 5.85%, down from 5.99% last week. Another $7 billion was sold in new six-month bills at an average discount rate of 5.85%, down from 5.96% last week. The rates were the lowest since April 14, when three-month bills sold for 5.84%, and since Sept. 2, 1977, when six-month bills averaged 5.84%. The new discount rates understate the actual return to investors--6.02% for three-month bills and 6.11% for six-month bills. The discount rate reflects the price discount received when government securities are purchased at less than face value.