A federal documents expert startled a Senate ethics hearing yesterday when he testified that neither Sen. Herman E. Tamadge (D.Ga.) nor his chief accuser, Daniel Minchew, signed a bogus Senate expenses voucher for $10,604 that ended up in a hidden bank account here in Tamadge's name.

Instead, said Treasury Department documents specialist Thomas Hundley, the evidence indicates that someone else-possibly one of two Talmadge aides who have not been previously implicated in any wrongdoing-might have been responsible for preparing the five-year-old voucher.

Hundley's testimony to the Senate Select Committee on Ethics, which is looking into five allegations of financial wrongdoing against Tamaldage, raised more questions than answers as the second week of testimony in the hearing came to an end.

With large blowups of Tamaldge's signature and the signature used on Tamaldgee's office automatic writing device, Hundley made these additional points to the committee.

A controversial 1974 memo indicating Talmadge was aware that campaign contribution to him were secretly being converted for his personal use was typed on a typewriter generally used by the senator's chief financial secretary. Allyne Tisdale. Tisdale denied under oath last week that she typed the memo.

The scrawled name, Harry P. Anestor, on an envelop that Talmadge's ex-wife Betty says contained a secret cache of $100 bills used by Talmadge was not written by Anestos, a Bethesda attorney and Tamaldge campaign supporter. Nor was it written by Mitchew, Hundley said. He did not test to see of Talmadge wrote it, he said.

Similar typeface irregularities and writing styles on memos linking Talmadge with money in the secret bank account indicate all the memos were typed by the same person in 1974 on the same typewriter-Tisdale's IBM electric machine. But Hundley stopped short of saying that Tisdale typed the memeo.

A total of $39,000 in illegal Senate reimbursements, cash gifts and mostly unreported campaign contributions went into the secret account at the Riggs bank in 1973 and 1974. Minchew has acknowledged that he opened the account and deposited the money. But he said it was done with Talmadge's approval and the senator ended up with some of the money from the account.

Talmadge has denied knowledge of the account and has called Minchew "a proven liar, thief and embezzler."

Yesterday's testimony by Hundley and documents he submitted to the committee are the first evidence the ethics panel has obtained that someone besides Minchew may have been responsible for funneling money into the secret account.

According to Hundley the signature, "Herman E. Tamaldge," on the $10,604 Senate reimbursement voucher submitted by Talmadfe's office for non-existence or unreimbursable expenses could have been written by either Tisdale or T. Rogers Wade, who succeeded Minchew as Talmadge's administrative assistant

But, said Hundley, Minchew could not have forged the signature. "In my opinion, I do not believe he has the graphic skill to produce such a signature," Hundley said.

Hundley said his examination of other handwriting samples from persons in Talmadge's office indicated that both Wade and Tisdale did have the "high degree of writing skill" which would have enabled them to duplicate Talmadge's signature. He did not, however, accuse either one of having done so.

Talmadge, visibly angry over another matter, disrupted the opening of yesterday's hearing. The Georgia senator, who has spent most of the nine days of testimony sitting quietly and puffing a long cigar, jumped to his feet to protest a procedural ruling by the committee chairman, Sen. Adlai E. Stevenson III (D-Ill.).

In a heated exchange, Stevenson ordered Talmadge to refrain from talking about his case-Talmadge has not yet allowed himself to be placed under oath by the committee-and Talmadge insisted on being recognized as a "U.S. senator from Georgia."

The dispute-over whether opposing attorneys can cite testimony given during closed prior approval from the ethics panel-was resolved to everyone's satisfaction after an hour's delay. The committee ruled that secret testimony can be cited during questioning of witnesses who gave that testimony. CAPTION: Picture, Sen. Talmagde confers with one of his attorneys during a break in the hearing. By James K. W. Atherton-The Washington Post