John W. Nields Jr., the chief attorney for the House committee investigating South Korean influence-buying, should be disciplined for commenting improperly on charges pending against Rep. John J. McFall (D-Calif.), three of McFall's home state colleagues have charged.

In a Friday letter to Rep. John J. Flynt Jr. (D-Ga.), chairman of the House Committee on Standards of Official Conduct, Reps. John E. Moss, B.F. Sisk and Harold T. (Bizz) Johnson, all California Democrats, asked that Nields be punished and barred from further participation in the disciplinary proceeding against McFall because of comments Nields allegedly made to a reporter.

McFall has been accused of breaking House rules by taking $3,000 in cash from South Korean businessman Tongsun Park, failing to report the money and making personal use of it after the funds were deposited in a secret office account.

Nields presented the evidence against McFall in three days of public hearings during the past two weeks. Final committee arguments in the case are scheduled for Wednesday.

It is possible an investigation of the complaint againt Nields could delay final consideration of the McFall case past the Nov. 7 election.

The allegations against Nields were prompted by a report in last Wednesday's Stockton, Calif., Record by reporter Doug Underwood. It contains only one direct quote from Nields. It is not clear exactly which indirect statements attributed to the attorney came from the public testimony and which from an interview.

The letter filing the formal complaint against Nields cites statements attributed to the committee lawyer giving out for prosecution. The letter said such statements violate the attorney's code of ethics and committee policy about not commenting on pending disciplinary cases.

Nields' conduct, according to Moss, Sisk and Johnson, "is contemptible and seriously impugns the integrity of the ongoing proceedings."

Nields said in a phone interview yesterday that "95 percent" of the statements attributed to him in the article came from the public hearings. He said he did answer a question from the report on why the committee had not proceeded against some other House members.

Nields said he felt he had broken no rules.

Flynt said yesterday that he couldn't really discuss the complaint because it would be brought before the committee early this week. But he said, "Any time you discuss a pending matter, you tend to go beyond the facts and give your own views and opinions."

Flynt added that he hoped the matter could be settled quickly. Asked if McFall's case might have to be postponed beyond the election, he said, "Nobody wants that, least of all John McFall." McFall could not be reached for comment yesterday. Administrative assistant Sam Mabry said he was not aware how McFall's three colleagues learned of the Stockton Record article. He did note that Johnson's office is next door to McFall's.

McFall's attorney, Carole Kuebler, said yesterday that she had sent a similar letter of complaint to the committee last week.

"Mr. Nields never chose to reveal to us through discovery the reasons for the committee's actions against Mr. McFall. He chose insteadto reveal it to a reporter."

The committee voted last week to recommend to the full House disciplinary action against two other California Democrats because of their dealings with Park.

The committee decided to recommend "censure" of Rep. Edward Roybal and a "reprimand" of Rep. Charles H. Wilson.

Roybal was found guilty of lying about and converting to his own use a $1,000 cash gift he accepted from Park in 1974. Wilson was found guilty of making a false statement to committee investigators about cash he received from Park as a "wedding present" in 1975.

This week's scheduled final arguments in the cases against McFall and Rep. Edward Patten (D-N.J.) are the last in the committee's Korean investigation. CAPTION: Picture 1, REP. JOHN I. McFALL . . . accused on $3,000 gift from Park; Picture 2, REP. JOHN J. FLYNT JR. . . . hopes issue can be settled quickly