A Treasury Department documents expert said yesterday that two 1974 memos linking Sen. Herman E. Talmadge (D-Ga.) with a secret bank account containing improper Senate reimbursements and diverted campaign funds apparently were typed by Talmadge's financial secretary.

Treasury Department specialist Thomas Hundley told the Senate Select Committee on Ethics that the memos bore all the stylistic traits of Talmadge's financial aide, Allyne Tisdale. Hunley testified previously to the committee that the notes were typed on Tisdale's typewriter.

Under cross-exanination, however, Hundley acknowledged that another former Talmadge aide, Daniel Minchew-now the senator's chief accuser-also could have typed the memos if he used Tisdale's typewriter and copied her style.

The memos concern contributions allegedly diverted from the Talmadge's Senate campaign in 1974 for his own use. Tisdale has denied under oath to the ethics panel that she wrote the memos. Talmadge has said he did not divert campaign contributions to his personal use.

The ethics committee began its fifth week of testimony on the case yesterday. The committee originally estimated it would take two weeks to hear all the testimony relating to five charges of financial misconduct against Talmadge. But it now appears the hearings will last up to two months.

In other testimony yesterday, Minchew, who was Talmadge's chief aide from 1971 through most of 1974 said that each time he put improper Senate expense reimbursements into the secret bank account, he first conferred with Talmadge.

Testimony last month before a 10 day recess in the committee's hearing, Minchew said that Talmadge was aware of the secret account and profited from it. Federal auditors have traced about $16,000 from the account to Minchew but have been unable to account for $17,000 more that was withdrawn on checks made out to cash and endorsed with Talmadge's automatic pen.

Talmadge has denied any knowledge of the account until last year and had said he did not get any money from it. He has accused Minchew of embezzling the money.

The Ethics Committee says it has "substantial credible evidence" of financial wrongdoing by Talmadge in all five allegations against him. Thus far, however, the committee has produced little to support the charges beyond Minchew's testimony and backup documents supplied by Minchew.

During yesterday's session, Talmadge's attorney James Hamilton, sought to shake Minchew's version of how he handled a series of campaign checks diverted into the secret account. In all, about $26,000 in mostly unreported contributions and $13,000 in separate reimbursements were funneled into the account.

Minchew said he diverted the campaign checks either on Talmadge's direct order or on his own. In the latter case, he said, he later told Talmadge of the diversion.

Minchew disputed several points in the testimony given by contributors whose checks were diverted. He said that while none of the contributors had evidence to support their version of the conrtributions, he had documents to support his story.

The committee is expected to hear additional testimony from Minchew through much of this week.