Senate investigators have obtained a copy of a 1974 memo to Sen. Hermac E. Talmadge (D-Ga.) referring to a $5,000 political contribution to Talmadge from a Georgia businessman. The money ended up in a secret bank account here that Talmadge says he never knew of until this year.

The memo was written to Talmadge by his former chief aide. Daniel Minchew, according to knowledgeable sources. It refers to a contribution from J.C. (Bud) Shaw, a Dalton, Ga., carpet manufacturer, the sources said.

The money was deposited in a secret account opened by Minchew in 1973 at the Riggs National Bank here. The account through which a total of $39,000 in illegal Senate reimbursements and diverted campaign contributions was funneled in 1973 and 1974, was in Talmadge's name.

Minchew, in his private appearances before the Senate Select Committee on Ethics, has presented the memo and others as evidence that Talmadge knew of the diverted contributions and the account. Talmadge has asserted that he did not know of the contributions or of the secret account until July of this year.

Talmadge and Minchew are under investigation by the Senate committee and a federal grand jury here over allegations concerning the account and Talmadge's other financial affairs. Talmadge is also being investigated by the Internal Revenue Service on similar allegations.

Sources said yesterday that Minchew testified two weeks ago that he used the memo to remind Talmadge of the contribution from Shaw. The $5,000 contribution to Talmadge has been confirmed by Shaw, who has told Senate investigators he made a legitimate campaign donation and that he has a copy of the canceled check.

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Talmadge, in a statement released yesterday by his press spokesman, Gordon Roberts, said he did not recall ever seeing the memo. "I see scores of memoranda each month," Talmadge said. But Roberts said he could not absolutely deny that the Minchew memo had been written.

Several other memos relating to Talmadge campaign contributions were also turned over to Senate probers by Menchew, according to knowledgeable sources.

The sources said Minchew made available memos showing an exchange of messages in 1974 between himself and Allyne D. Tisdale, Talmadge's secretary and campaign treasurer. The messages, whose authenticity has been challenged by Tisdale, allegedly concern money diverted from contributions to Talmadge's 1974 Senate reelection campaign.

According to the sources, one memo contains a typewritten exchange of messages between Minchew and Tisdale about a $2,000 contribution that was deposited in the select account.

In the memo dely the same day as deposit, Tisdale asks for $500 for Talmadge's personal use, apparently from a legal $2,000 contribution given by Texas Oilman Howard B. Keck in the form of four $500 travelers check, according to the sources. The rest of the money was locked up in a cabinet in Talmadge's Senate office suite, sources said bears both Minchew's vestigators. The second memo, which sources said beas both Minchew's typed name and Tisdale's typed initials, contains a notation allegedly typed by Tisdale that two other contributions totaling $550 were never reported as required by law.

Sources said a contribution for $50 was made by Macon, Ga, businessman, Ted Lamis. Lamis reportedly told the Washington Star he gave the money in cash to Talmadge at Talmadge's estate in Lovejoy Ga. Lamis could not be reached for comment yesterday.

In a statement, Talmadge said his staff uncovered an unitemized contribution to his 1974 campaign for $50 and it was trying to determine yesterday if the money came from Lamis.

The second envelope allegedly contained a typed notation showing the figure $500 and the identification "various Coca Cola (Earl Leonard)."

A Coca Cola Co. spokesman in Atlanta said yesterday that Leonard, who is the company's vice president for public affairs, testified before the Senate Ethics Committee staff Monday that he never made any contribution to Talmadge in 1974 or handled a contribution for other employes of the firm.

In a statement yesterday, Talmadge denied receiving money from Leonard. The statement said Tisdale had testified under oath she never saw the memo. Tisdale has also said she believed the memos given to the committee by Minchew were fabricated by the former aide.

Senate investigators have determined that the memos given them by Minchew were typed on machines used by Minchew and Tisdale. A spokesman for Talmadge said yesterday that Minchew took his typewriter with him when he left Talmadge's staff in late 1974 and Tisdale's typewriter was traded in to the General Services Administration after the memos were allegedly written.