Yields on 30-year Treasury bonds fell in yesterday's auction to the lowest level in nine months as the government concluded its biggest-ever, $34.25 billion quarterly refunding.

The average yield was 8.71 percent, down from 8.87 percent at the last auction on Aug. 9.

It was the lowest rate since 30-year bonds averaged 8.50 percent on Feb. 8. The bonds will carry a coupon interest rate of 8 3/4 percent with each $10,000 in face value selling for $10,037.60.

The bidding for the bonds slackened somewhat from the pace of Tuesday's and Wednesday's auctions of three-year and 10-year bonds, and the decline in rates was not as great, in part because of the greater risk associated with the longer terms.

A total of $10.75 billion in bonds were sold yesterday out of bids totaling $22.08 billion.

The Treasury also yesterday sold $12 billion in 161-day cash management bills with an average discount rate of 7.08 percent.

The discount rate understates the actual return to investors: 7.41 percent with a $10,000 bill selling for $9,683.40. In addition, the Treasury sold $9.8 billion each in three-month and six-month bills at its weekly bill auction on Monday.

The refunding included the sale of $12.6 billion in three-year notes on Tuesday and $11.1 billion in 10-year notes on Wednesday.

This quarter's refunding is $2 billion larger than the previous record, set last August.

The notes and bonds are sold regularly during the large debt auctions held four times a year to replenish the government's coffers.