The indictment yesterday of Rep. Charles C. Diggs Jr. (D-Mich.) will have no effect on his official standing as a member of Congress or as chairman of the House District Committee.

The House's code of official conduct suggests that members convicted of a crime for which a sentence of two or more years may be imposed "should refrain" from voting or participating official business. But the code makes no mention of an indictment, which is merely the formal placing of a charge by a grand jury.

From a practical point, the indictment could diminish the reputation of an elected official and, as one congressman who did not wish to be identified said, it "will surely hurt the District Committee, the Black Caucus and all of Congress."

Edward C. Sylvester Jr., staff director of the District Committee and a longtime personal friend of Diggs, said the charges will have "no effect" on operations of the committee.

Sylvester noted that "there have been rumors about the indictment for a year, and through all of that it made no difference in the functioning of the committee."

At the committee offices on the third floor of the Longworth House Office Building yesterday afternoon, staff members went ahead with a going away party for an employe who is moving to Africa with her husband. But the mood appeared to be reserved.

Sylvester said he was "absolutely sure" that five of the persons named in the indictment as having received inflated congressional salaries from Diggs were "never on the payroll."RTThe exception was Jean G. Stultz, who is listed in the report of the clerk of the House as having been secretary to Diggs as committee chairman, and at the same time, for a while, as legislative secretary on his congressional staff.

"It's never been against the rules to be on more than one payroll" Sylvester said.

The selection of committee chairman is a function of the House Democratic Caucus, which is made up off all Democrats in the House.

A staff employe of the caucus said yesterday that "no one has suggested" that any more be initiated to strip Diggs of the job he got in 1973 following the election defeat of the committee's long-time chairman, Rep. John L. McMillan (D-S.C.).

Technically, the House has the right to expel a member whose conduct is "inconsistent with the public trust and duty of a member," But that broad power has been invoked only three times, all of which involved treason in 1861.

Historically, according to a report of the Committee on Standards of Official Conduct, it has been the eustom to defer action until any criminal proceeding has been completed.

William P. Arbogast, assistant staff director of the committee, said "sometimes members under indictment have voluntarily refrained from voting."

He also recalled that two members lost chairmanships although they had not been convicted of crimes.

In 1966, the House Education and Labor Committee adopted new rules that resulted in stripping its chairman, Rep. Adam Clayton Powell (D-N.Y.), now deceased, of much of his power. The action occurred before the issuance of a report later that year which said Powell had used congressional funds for personal travel.

On Jan. 27, 1977, the House Democratic caucus voted to strip Rep. Robert L. F. Sikes (D-Fla.) of his chairmanship of the military construction appropriations subcommittee. Sikes had been officially reprimanded earlier after the House ethics committee found that he had been involved in a conflict of interest and had failed to file required information on his financial report.

Rep. Ronald V. Dellums (D-Calif.), the ranking Democrat on the District Committee, said it was "not appropriate to comment) on Diggs's indictment.

Rep. Stewart B. McKinney (R-Conn.), ranking minority member, said he hopes the work of the committee "will go ahead."

"The whole committee cares about the city, and that's what is important," McKinney said.