The interest rate on All Savers certificates, based on yesterday's auction of one-year Treasury securities, will drop from 10.77 percent to 8.34 percent next week, the biggest decline since the certificates were introduced Oct. 1 with a rate of 12.61 percent.

Depositors can take advantage of the current 10.77 percent rate through Nov. 28.

Married persons filing jointly have the right to exclude from federal income taxes $2,000 in interest paid on these certificates; single persons, $1,000. Sales of these certificates are scheduled to continue until the end of 1982, but the exclusion can be taken only once during that period.

To take maximum advantage of the exemption, couples would have to deposit $23,980 at the new rate; single persons, $11,990. To benefit from these tax exempt investments, persons should be in at least the 30 percent tax bracket. The certificates are usually sold in $500 denominations and have a maturity of one year. Premature withdrawal results in a loss of interest and the tax exemption.

All Savers certificate rates equal 70 percent of the average annual investment yield on one-year Treasury securities. At yesterday's auction that rate plunged to 11.92 percent. The discount rate was 10.506 percent and the coupon equivalent yield 11.58 percent. The average return was down from 13.16 percent at the previous auction a month ago and was the lowest since 9.97 on Sept. 10, 1980. The Treasury accepted bids for $5 billion in one-year bills.

Since Sept. 15 the discount rate on one-year bills has fallen by 4.5 percentage points. The next auction will take place in a month.

The All Savers Act was intended to help the ailing thrift industry and to encourage savings. Before its passage widely differing estimates were made on the expected volume of sales. The Joint Tax Committee projected a low of $65 billion. The Treasury chose a middle figure of $120 billion, and the U.S. League of Savings Associations, a thrift industry trade group, said it would reach $228 billion.

During the first month sales amounted to $35.4 billion. However, this figure cannot be used as a monthly average to project total sales because heavy initial buying has tapered off. For example, sales in the first 10 days reported by the Federal Home Loan Bank Board were $11.6 billion, but just $4.9 billion in the following 20 days.

According to statistics released by the bank board and the Federal Reserve, commercial banks captured 36.2 percent of the $35 billion deposited, while all thrift institutions had a 63.8 percent share.