WASHINGTON (AP) _ The House ethics committee Wednesday formally charged Rep. Austin J. Murphy Jr., D-Pa., with six counts of violating House rules involving misuse of public funds and allowing someone else to cast his votes during absences from the House floor.

The panel also announced without comment that it will conduct preliminary investigations of alleged wrongdoing by Democratic Reps. Mario Biaggi of New York and Richard H. Stallings of Idaho.

The initial inquiry on Biaggi came one day after the 10-term congressman from the Bronx was convicted in federal court in Brooklyn, N.Y., of illegally accepting gratuities from a Brooklyn political boss, illegal interstate travel and obstruction of justice.

House ethics rules require the panel, formally known as the House Committee on Standards of Official Conduct, to conduct an investigation automatically when a member is convicted of a crime carrying a penalty of more than one year in prison. Biaggi could be sentenced to 12 years in prison.

The preliminary inquiry on Stallings, a two-term congressman, was triggered by allegations that his campaign committee made $5,800 in loans this year to Stallings and a staff aide.

Stallings had said earlier that both loans were listed on his current House financial disclosure form, and that he had verbal assurances from the Federal Election Committee that both transactions were proper.

Through spokeswoman Melodie Rydalch, Stallings said:

''I am not surprised that the committee has decided to conduct a preliminary inquiry into loans made by my campaign committee earlier this year.

''At the time the loans were made, I was satisfied that the loans were proper and disclosed in accordance with applicable law. When questions arose about their propriety, I expressed my intention of ensuring that these loans fulfilled all legal standards.

''Accordingly, I welcome the opportunity to work with the committee to resolve any doubts about the loans. In fact, I have already contacted the committee to ask for prompt resolution.''

A spokesmen for Biaggi, reached by telephone, had no immediate comment on the ethics panel's action.

''We obviously have not had an opportunity to fully review, analyze and prepare a full response to the alleged violations,'' said a statement released by Murphy's office. It noted that he has 21 days to respond.

The statement also said Murphy ''is confident that when we have an opportunity to present a full and thorough reply to the specific allegations, the committee will conclude that there has been no violation of House rules.''

Murphy spokesman Fred McLuckie said the congressman appeared before the panel during the summer at his own request. He said Murphy was allowed to speak, but was not asked any questions by the panel.

The committee announced it had served a ''statement of alleged violations'' on Murphy, a six-term congressman.

The panel said the statement means there is ''reason to believe'' that Murphy had violated House rules or the code of official conduct for House members, setting in motion a process to determine whether sanctions should recommended for House action.

The six-count statement charged that twice in 1978 and once in 1982 while Murphy was absent from the House floor, he allowed another person to cast votes in his name, in violation of House rules.

Murphy also was charged with diverting government property, including furniture, photocopy services, supplies and long-distance telephone service, from his congressional district office in Charleroi, Pa., for use by his local law firm.

''Individuals with whom (Murphy) had a professional or legal relationship directly benefited monetarily from the expenditure of official allowances'' in violation of House rules, the panel said.

The statement said Murphy also violated the House ethics code by hiring Michael Corbett for a job on a House Education and Labor subcommittee in 1981 and 1982, ''notwithstanding the fact that (Murphy) knew that Mr. Corbett did not perform duties commensurate with the compensation he received.''