Most Washington area financial institutions are planning to offer the new 2 1/2-year certificate of deposit that makes its debut today.

The certificate, which will be sold in denominations as low as $100, will enable small savers to receive over 10 percent interest on their money.

A random telephone survey of 10 savings and loan associations and 10 banks revealed that all of the savings institutions and 80 percent of the banks questioned intend to sell the new certificate.

Four out of five thrifts have set their minimum requirements at $100. Perpetual, the area's largest savings and loan, has established a minimum of $1,000. Jefferson Federal says it will offer a three-year certificate at the 2 1/2-year rate.

Of the banks surveyed, two replied they were still undecided whether to offer the ceritificate and another had not yet set its minimum deposit. Those responding all said they would charge $500, except Dominion National which will open a 30-month account for just $100.

The interest rate is determined by that of Treasury securities of the same maturity and is subject to change once a month for new issues. The initial certificates sold by thrifts will have a rate of 10.4 percent; those by banks will pay 10.15 percent. Compounding is permitted.

Federal financial regulators announced the new certificate in mid-December. It is expected to be more popular than four-year certificates -- last year's first attemt to offer small savers market rates -- because it does not require people to tie up their money for as long.

Also, the four-year certificate was introduced at a time when interest rates were still rising.

"In order for this (2 1/2-year certificate) to have a significant impact, there must be a broad public perception that interest rates are past their peak and on the way down," said Saul B. Klaman, president of the National Association of Mutual Savings Banks.

These new variable-rate certificates, along with the recently announced short-term renegotiated mortgage, are designed to restore stability to the housing market by increasing savings deposits and thus boosting the amount of money available for mortgages.