A government auditor said yesterday that he traced $12,855 from a secret bank account in the name of Sen. Herman E. Talmadge (D.-Ga.) to Talmadge's former chief aide, Daniel Minchew.

But Lawrence Sullivan, an assistant director of the General Accounting Office on loan to the Senate Select Committee on Ethics, said a term of financial sleuths was unable to account for nearly $21,000 in improper Senate expense payments and campaign reimbursements that was also deposited into the secret account at the Riggs National Bank here and later withdrawn.

Minchew has told the Ethics Committee in executive session that during 1973 and 1974 he set up and ran the bank account with Talmadge's approval. He has also told the committee that he got some of the money from the now dormant account, but that the bulk of it went to Talmadge.

The Ethics Committee is investigating five charges of financial misconduct against Talmadge. The most serious of the charges involves filing false expense claims with the Senate and converting campaign contributions to his own use through the secret bank account.

Talmadge has denied the charges, and has emphatically rejected any knowledge of the Riggs account before it was raised in newspaper accounts last year. At the opening of the ethics hearings nearly three weeks ago, he accused Minchew, who was his chief aide until October 1974, of embezzling money and of lying.

Obviously chafing at the slow pace of the hearings, Talmadge told reporters outside yesterday's Ethics Committee session that the procession of accountants, campaign contributors and others who have appeared so far is "a waste of the taxpayers' money."

"The real issue," Talmadge said, "is who opened the Riggs account, who had knowledge of it and who stole the money."

Ronald Wertheim, a member of Talmadge's defense team, yesterday sought to establish from Sullivan that some of the money in addition to the $12,855 traced by Sullivan may have gone from the secret account into Minchew's personal account.

Wertheim said an analysis of Minchew's bank records showed numerous deposits of small checks in multiples of $10. The checks were paychecks for congressional interns which Minchew cashed for them and then deposited in his account, Wertheim said.

"That might have been considered a way of laundering some of the secret account money before it got transferred to his account," Wertheim suggested.

Talmadge's attorney noted that Sullivan had not been able to trace the source of deposits of under $1,000 into Minchew's account from 1973 to 1976. Some of these smaller deposits, the lawyer said, could have come from the secret account.

Sullivan acknowledged that the money-washing hypothesis was possible. But, he added, "In my opinion it doesn't make sense."

A more likely possibility, Sullivan said, was that the source of the deposits of under $1,000 were rent payments from Minchew's property holdings and his travel reimbursements. The amounts of money from these two categories, Sullivan said, nearly equalled the total of the smaller deposits.

According to Ethics Committee records released yesterday, the total amount deposited in the secret account came to $39,314. The account had a balance of $113 when it became dormant in late 1974.

Sullivan said it was possible that Minchew got all the money in the secret account. But Minchew's habit of taking out small loans and writing checks to cash was "inconsistent with someone who has a cash horde," he said.

The Senate auditor said he traced $6,600 from the secret account to Minchew's account. More of the secret account cash was used by Minchew to pay for repair work on his real estate holdings, he said. Sullivan said Minchew also converted $4,700 from the secret account and held it for four months before returning the money to a legitimate Talmadge campaign account.

All of the withdrawals from the secret account were by checks made out to cash with Talmadge's name endorsed on the back by the senator's automatic writing pen, said Sullivan.

The Ethics Committee hearings are scheduled to resume Monday, with Minchew as the witness. CAPTION: Picture, Lawrence Sullivan checks his charts during his appearance before the Senate Select Committee on Ethics. By James K. W. Atherton - The Washington Post