Two witnesses yesterday contradicted earlier sworn secret testimony from the chief accuser in Sen. Herman E. Talmadge's financial misconduct case about the way they delivered campaign contributions to the senator.

H. P. Williams, a retired Maryland frozen food processor, told the Senate Select Committee on Ethics that testimony given earlier by Daniel Minchew about his 1974 contribution to Talmadge was "nothing but a plain, outright fabrication."

A second witness, oil lobbyist Robert Schramm, also denied Minchew's account to the committee about the way he delivered $2,000 in traveler's checks that was contributed to Talmadge by a Houston oilman.

Their testimony marked the second straight day that witnesses have appeared before the ethics panel challenging Minchew's truthfulness. On Tuesday, FBI polygraph experts said they found Minchew apparently lied when he said Talmadge knew of a secret bank account containing illegal Senate reimbursements and mostly unreported campaign contributions.

Minchew's credibility is a key issue in the case against Talmadge. Thus far, Ethics Committee attorneys have produced little evidence to support their five allegations of financial wrongdoing by the senator beyond that provided by Minchew.

Minchew, who left his job as chief aide to Talmadge in 1974, is expected to testify before the committtee early next week.

Williams, 62, said he had not seen Talmadge since 1945 but sent him $500 campaign checks on a sporadic basis because "I tried to support the people who did the job as I would have done it."

Under questioning by Talmadge's lawyer, Williams flatly denied periodically driving to the senator's office here from his home in Trapp, Md., and leaving envelopes full of cash for Talmadge.

"Any man who states that I ever gave to Sen. Talmadge or to any member of his staff or to any member of his family as much as one cent in legal tender or legal specie is lying," Williams said.

According to knowledgeable sources, Minchew testified twice last fall before the committee's investigators. In the first session on Sept. 28, Minchew, who was not under oath, described Williams as "a man who had a reputation for coming by the office and leaving an envelope full of money or sending checks through the mail."

In sworn testimony Oct. 4, Minchew told the same Senate investigators that Williams "at times left significant amounts of cash in envelopes in the office." The sworn testimony did not mention Williams sending checks.

Later during the Oct. 4 testimony Minchew said "pat Williams is a man who in the past has given cash and sometimes large amounts of cash . . . . He used to live in Maryland and would drive in and leave envelopes with cash in them."

Schramm, who worked for Talmadge from 1966 to 1969, was an oil lobbyist in 1974. He said Minchew was incorrect when he testified that Schramm called him in 1974 about making a contribution for "one of his principals."

Minchew testified under oath to the committee that Schramm later visited Talmadge in his office and left $2,000 with the senator. According to Minchew, Schramm later stopped by Minchew's office to tell him of the contribution.Minchew's testimony quotes Schramm as saying "I just wanted you to know that I delivered the money."

Schramm denied yesterday that the meeting with Minchew ever took place.

Schramm said he could not recall ever supplying four $500 traveler's checks to Talmadge in 1974 but did not deny the donation. The money was given on behalf of Robert Keck, head of the Superior Oil Co. and Schramm's boss at the time.

Williams and Schramm were among six persons who testified yesterday on financial contributions to Talmadge's 1974 campaign. The contributions allegedly ended up in the secret bank account that is one focus of the charges against Talmadge. CAPTION: Picture, Sen. Herman E. Talmadge (D-Ga.) before start of Ethics Committee hearing. AP