Daniel Minchew, chief witness in the Senate Select Committee on Ethics' investigation of Sen. Herman E. Talmadge (D-Ga.), wrapped up eight days of testimony yesterday, declaring that Talmadge was part of a scheme to siphon off Senate and campaign cash through a secret bank account.

But committee special counsel Carl Eardley, addressing the 39-year-old Minchew in a stern voice, noted that the former Talmadge aide had been shown during the case to have been "deceptive in some of your business relations."

"As a consequences," Eardley said, "your credibility as a witness has been eroded."

Minchew has acknowledged in his testimony that he withheld money from a real estate coinvester and that he diverted at least $18,000 to himself from the secret account in Riggs National Bank.

So far, however, Minchew, who was Talmadge's chief aide until 1974, has been Eardley's only direct witness against the veteran Georgia senator. The other witnesses during the five weeks of testimony have either been talmadge staff members sympathetic to their boss or expert witnesses called to corroborate specific points.

In rapid fire order at the close of Minchew's appearance yesterday, Eardley led his witness through the allegations against Talmadge. Did Talmadge know of padded expense vouchers diverted to the secret account? Did the senator know campaign contributions also went into the account? Did Talmadge know Minchew was helping himself to the money also? Did Allyne Tisdale, another Talmadge aide, prepare memos implicating Talmadge in the scheme? And did Minchew deliver money from the secret account to Talmadge and the senator's late son, Bobby?

In each case, Minchew answered, "Yes sir."

The senator's former wife, Betty, is scheduled to appear before the committee today to testify that Talmadge kept a roll of $100 bills in old overcoat in their Washington apartment until they separated in 1974.In April she turned over 77 of the $100 bills to the committee and investigators have traced them to a bank in Texas.

But the committee has apparently not been able to link the bills directly to Talmadge or to the Riggs accounts. The remaining list of witnesses to be called by Eardley contains no bank officials who might testify to such a linkage.

The committee is also scheduled to hear from Harry P. Anestos, a Talmadge supporter whose name was on the envelope that Betty Talmadge says contained the $100 bills. A federal handwriting expert has told the committee Anestos did not sign his name to the envelope, adding to the mystery of the cache of big bills.

The only other witness scheduled to be called is Phyllis Stambler, a sales clerk from a Lord & Taylor outlet here. She is expected to confirm that Betty Talmadge made purchases in the store using $100 bills. The senator's former wife claims they were given to her by Talmadge.

Talmadge has denied any knowledge of the secret bank account. In his opening statement, which was not under oath, Talmadge told the committee his attorneys would prove that the packet of $100s did not come from the secret account. He also said they would show the packet could not have been in his overcoat in 1974.

Thus far in the long-running case, the issue of the $100 bills has remained virtually untouched by either side. Talmadge's attorneys have, however, obtained testimony from the senator's aides that his former wife was subject to excitable and erractic behavior.

In yesterday's testimony Sen. Harrison Schmitt (R-N.M.) became the second committee member to question openly Minchew's lack of support for his assertion that Talmadge knew about the secret Riggs account and benefited from it. Earlier, Sen. Jesse Helms (R-N.C.) voiced a similar concern. CAPTION: Picture, Daniel Minchew closes his briefcase after winding up eight days of testimony. By James K. W Atherton - The Washington Post