Rep. Frederick W. Richmond (D-N.Y.) has been negotiating with the Justice Department on a possible guilty plea to a federal income tax charge, but an agreement has been delayed because officials here want more serious charges added, according to sources familiar with the investigation.

Richmond has offered to plead guilty to a charge involving a false statement on his tax returns, the sources said. He would still be able to run for a fifth term in the House, since the Constitution doesn't bar people convicted of crimes from holding federal office. Richmond filed papers last week for New York's Sept. 23 primary.

But Justice Department officials say a single-count plea without acknowledgment of other illegal conduct isn't enough, sources said. A federal grand jury in Brooklyn has been investigating Richmond on allegations involving drugs, campaign violations and aiding a fugitive.

"Our concern is, is he pleading guilty to enough?" one official said. "Or would he be getting off on a socially acceptable charge of falsifying his tax returns ?"

It could not be learned what the government is willing to settle for. Sources said department officials had approved seeking an indictment of Richmond on multiple counts if the plea bargaining failed.

U.S. Attorney Edward R. Korman in Brooklyn and Walter S. Surrey of Washington, one of Richmond's attorneys, declined to comment. Kalmon Gallop of New York, who sources said is handling the plea discussions for the congressman, could not be reached.

Officials refused to outline the potential tax charge. There have been reports that the grand jury heard evidence that Richmond's corporation paid for some of his personal living expenses. And a federal judge in St. Louis ruled last fall that Richmond's retirement from the Walso National Corp. he founded was "feigned" so that he could receive a $1 million "pension."

The grand jury also has been investigating allegations that the 58-year-old Richmond paid aides to buy drugs for his personal use, that he used his company's employes in his campaigns and that he arranged for an escaped felon to get a job in the House.

In 1978 Richmond was charged with sexual solicitation of an undercover police officer and a teen-age boy in Washington. The charges were dismissed when he agreed to receive professional counseling.

The congressman has a liberal voting record and has championed the food-stamp program as chairman of the House Agriculture subcommittee on nutrition. Richmond had promised to make one more effort to prevent sharp budget cuts on food stamps, but he was absent from a final budget reconciliation conference yesterday.

The House ethics committee also is investigating Richmond. A guilty plea wouldn't necessarily solve his problems there. But if he reached agreement with the Justice Department on some sort of guilty plea before New York's congressional primary next month and were renominated and reelected, he could argue that his constituents voted with full knowledge of his plea and that the House, therefore, shouldn't interfere.

Former representative Charles Diggs (D-Mich.) was reelected in 1978 despite a payroll-kickback conviction. Censured by the House in 1979, he did not resign until 1980, when the Supreme Court rejected his final appeal.