The Senate Ethics Committee has formally sought immunity from prosecution for the former administrative aide to Sen. Herman E. Talmadge (D-Ga.) in return for his testimony on the Senator's finances.

The committee's grant of immunity sought in papers filed with Chief U.S. District Court Judge William B. Bryant, will be delayed 20 days because the Justice Department invoked its right to postpone immunity. At the end of the 20 days, according to committee spokeswoman Lyn Murphy, the former aide, Daniel Minchew, will be interviewed by the committee staff and then questioned under oath by the committee.

Talmadge has acknowledged that his name appeared on a secret account of nearly $40,000 that was active in the Riggs National Bank in 1973 and 1974. Talmadge has emphatically denied knowing about the bank account until told by his staff.

Minchew left his staff in 1974 and now is a member of the International Trade Commission.

Sources close to the investigation said earlier this week that a lawyer for Minchew has told Senate investigators that Minchew has receipts that will show some of the money from the secret bank account were used to pay for repairs on Talmadge's car.

Papers drawn as part of the committee's request for immunity for Minchew indicate that he is expected to invoke his constitutional right against self-incrimination. The grant of immunity - so-called "use immunity" - bars prosecutors from using his testimony against him in a prosecution, unless perjury is committed. The immunity grant also compels the witness to answer questions.

Justice Department officials declined to say why the delay was being sought In the past, prosecutors have used the delay to prepare evidence and testimony against a witness called before a congressional committee. The evidence then can be presented to a federal judge, under seal, so that prosecutors can later demonstrate that they obtained evidence against a witness they wish to prosecute without using his testimony.

Sources familiar with the secret bank account said earlier this week that between $5,000 and $6,000 of the almost $40,000 in the account had been transferred by Minchew to his personal account in the bank. About 40 checks, each written to cash and each signed with Talmadge's aultomatic pen signature machine, were written on the account, which still contains about $113.

Minchew has said that nearly $13,000 in the secret account was obtained by him when he filed for Senate reimbursements of improper expense claims. The remainder of the money came from Talmadge campaign contributions, according to sources. Investigators are trying to determine whether the campaign receipts in the Riggs account were properly listed in federal election reports.