After nearly a year of secret testimony and public silence, Daniel Minchew, the chief accuser of Sen. Herman E. Talmadge (D-Ga.), came into the open yesterday to tell a Senate ethics panel that Talmadge approved the illegal funding of a secret bank account and then benefited from it.

Minchew, 39, testified in clear, confident tones before the Senate Select Committee on Ethics that Talmadge was fully aware that he engineered the diversion of about $26,000 in Senate reimbursement checks for nonexistent office expenses and $13,000 in mostly unreported campaign contributions into the account in 1973 and 1974.

Minchew admitted that he, too, got some of the money in the secret account.

"My wrongdoing evolved out of misplaced loyalty," said the former aide, who left Talmadeg's staff in late 1974.

"I did things for which I am not proud and which were wrong," he said.

For nearly two hours yesterday, while Minchew testified, Talmadge with puffs of cigar smoke rising around his head in bursts, gazed straight across the Senate hearing room at his former chief aide. Minchew never returned the look.

Talmadge has denied any knowledge of the secret account and has called Minchew "a proven liar, thief and embezzler." He has not yet appeared under oath before the committee in his own defense.

Part of Minchew's allegations against Talmadge have become public through news leaks and, indirectly, through documents and three weeks of testimony from other witnesses called by the ethics panel.

But yesterday was the first time Minchew explained publicly how he went about converting campaign donations to Talmadge into cash.

In one case in 1974, he said, Robett Schramm, an oil industry lobbyist and former Talmadge staff member, delivered a $2,000 contribution from Houston oilman Howard Keck. Schramm left the money with Talmadge in the form of four $500 travelers checks, Minchew testified.

Talmadge's financial secretary, Allyne Tisdale, then relayed orders from the senator on how to handle the moiney, the former aide testified.

"Mrs. Tisdale said to me verbally that there were some travelers checks from Bob Schramm which had been given to Sen. Talmadge did not want deposited in the campaign account," Minchew said.

"I said to her there are ways we can get cash for those travelers checks," he said.

Minchew told the ethics committee that he wrote a memorandum to Tisdale advising her he would "take care" of the checks. She replied in a return memorandum on the same piece of paper, he said, that Talmadge wanted $500 and the rest was to be locked away in a cabinet in the office.

After he deposited the travelers checks in the secret account, Minchew said, he withdrew $2,000 in cash and returned to Talmadge's private Senate office.

"I handed him $500 and said Mrs. Tisdale would have the additional $1,500," Minchew said. He recalled that he locked the money into the cabinet according to Tisdale's instructions.

Talmadge has denied getting the money. Tisdale testified under oath earlier in the ethics committee hearing that she never wrote Minchew the note and never saw the travelers checks.

Minchew contradicted Tisdale and other Talmadge aids when he said that the Senator often carried $100 bills with him. Talmadgehas said he never carried large denomination bills and used small cash gifts from supporters for daily expenses.

Talmadge's former wife, Betty, who is scheduled to testify later in the hearing, has given Senate investigators seventy-seven $100 bills, which she said were part of a secret cache the senator shared with her and kept in an overcoat in their apartment here.

Minchew said that Talmadge also could be extremely money-conscious. "When he sent out for something to be bought and he paid for it he always counted the change," he said.

So far the major part of the Senate investigation of Talmadge has rested on the testimony Minchew gave in more than a half-dozen closed-door sessions with the committee's investigators since last summer. Minchew also has provided investigators with supporting documents whose admissability as evidence has been challenged by Talmadge's attorneys because they were taken without the senator's consent.

Minchew said that when reports of Talmadge's financial problems first appeared in the news last year, he had been "a participant in the plan to short-circuit and impede the investigation of Sen. Talmadge." He did not elaborate but he said that was no longer true.

In this open testimony yesterday Minchew said he first began talking with Talmadge about opening a secret account not long after he took over the job as Talmadge's administrative assistant in 1971.

"Senator Talmadge would say to me things about the difficulties of being a public official and the types of expenses one would have," Minchew said. "We discussed at one time the ways of sheltering money, of generating additional funds for him."

Minchew said he got a typewritten note indicating the millionaire Georgia senator needed more cash. He did not identify who wrote the note but said one of Talmadge's sons called him, also to ask for money for the senator.

The secret account, Minchew said, was one option he discussed with Talmadge as a means of raising the money. Eventually, he said, it was the option that was carried out.

Earlier yesterday Lawrence Sullivan, an accountant for the ethics committee, testified that auditors had traced $16,510 from the secret account to Minchew. Last week Sullivan said $12,940 was funneled to the aide, but yesterday he said additional work indicated the higher figure was probably correct.

The committee's investigators still have not traced $17,610 from the secret account. According to Minchew, the money was converted by him and others to the senator's use. Minchew suggested yesterday that among those who helped him in the scheme were other talmadge aides.

But he said that at no time was he fearful that the money diversion would be exposed by Talmadge.

"Why not" asked ethics committee chief counsel Carl Eardley.

"Because," Minchew replied, "he was fully aware of what was going on." CAPTION: Picture 1, Former aide Minchew: "I did things for which I am not proud . . . " By James K. W. Atherton - The Washington Post; Picture 2, Minchew, left, approaches witness table to state his accusations publicly. Center is attorney Robert Fierer. By James K. W. Atherton - The Washington Post