The chairman of the House ethics committee today barred the public and news media from the hearing on charges against Rep. Austin J. Murphy (D-Pa.), who said witnesses' privacy should be protected.

No member of the panel objected when Chairman Julian C. Dixon (D-Calif.) granted Murphy's motion to close the proceeding because it "may tend to defame, degrade and or invade the privacy of third parties."

However, Mark J. Davis, the committee counsel presenting the evidence against Murphy, argued that Murphy had not informed the committee which witnesses might be defamed, or how.

"For all we know, it is the congressman himself who would be defamed because he is the subject of the hearing," Davis told the panel before about 50 spectators and reporters were asked to leave.

The request to close the session was based on expected testimony surrounding two counts. One alleges that Murphy permitted congressional resources to be used at his former law firm. The other charges that he placed a "ghost employe" who did little work on a subcommittee payroll.

Murphy is also accused by the panel of having an unidentified House colleague vote in his name on the House floor.

Stanley Brand, the former House chief counsel who is Murphy's attorney, said three weeks ago that he saw no reason to bar the public from the hearing. Murphy aide Fred McLuckie said Murphy changed his stance because "several of the witnesses asked him if he would request a closed hearing."

"Considering some of these people are not his employes or associated with Congress, he felt it was incumbent upon him to respect their privacy," McLuckie said.

After the hearing, the committee of six Democrats and six Republicans was to vote on whether any charge against Murphy was proven. Later, the panel would decide on what penalty, if any, to recommend to the full House.

Davis said disciplinary hearings such as the one Murphy faced are rare. The last time the House took action against a member was in July 1984, when it reprimanded George V. Hansen, an Idaho Republican, for filing false financial disclosure forms. Hansen had already been convicted in court.

Murphy faces no criminal charges.

Attorneys for Murphy, who is in his sixth term, said in an Oct. 16 reply to the panel that "there is no allegation that the congressman sold his vote or misused campaign funds or was improperly influenced."

"Indeed, it is clear from the charges themselves that Congressman Murphy did not gain financially or politically from any of the conduct being challenged," they said.

Brand would not discuss what witnesses he would call on Murphy's behalf. But McLuckie said it was likely that Murphy would take the stand.