The chairman of the House ethics committee announced yesterday that E. Barrett Prettyman Jr., a prominent Washington lawyer, has been hired along with his firm, Hogan & Hartson, to run the investigation of potential bribery charges against seven House members implicated in an FBI undercover "sting."

Rep. Charles Bennett (D-Fla.) said Prettyman will begin immediately to determine how much cooperation and evidence the committee can expect from the Justice Department.

Meanwhile, Rep. John M. Murphy (D-N.Y.), one of those named in press accounts as having been videotaped discussing cash payments and legislative favors, tried to take the offensive yesterday. He lashed out at the Justice Department because of leaks in the case, demanded that the chief prosecutor be removed and asked that the tapes he turned over to his attorney immediately.

Prettyman said, "We're going to move ahead quickly but I can't talk about specific plans at this time."

Justice officials already have told the committee they have no intention of turning over their evidence -- including the videotapes and undercover witnesses -- until completion of any trials.

Some members of the committee noted the dilemma they face. On the one hand, they want to show they are taking swift action to pursue the charges. On the other, they don't want to be accused of obstructing the Justice investigation by court fights over the evidence.

"We really have to wait to work with the special counsel on his game plan," said Rep. Harold C. Hollenbeck (R-N.J.), referring to Prettyman. "But it would seem a first step would be for him to make a request at Justice on our behalf."

It also was learned that Prettyman will be asked to give the committee a legal opinion on whether it has a constitutional duty to try to move forward before the legal process at Justice is finished.

Bennett said Prettyman will be paid at the same rate as some previous special counsels, $100 per hour with a ceiling. His firm will provide assistance as needed.

It is expected that the committee will have to go to the House Administration Committee with a supplemental budget request. Rep. Frank Thompson (D-N.J.), one of those under investigation, is chairman of that committee.

Prettyman, 54, was an aide to Attorney General Robert F. Kennedy, served in the Johnson White House and has been president of the District of Columbia Bar. He also has represented news organizations and the Reporter's Committee on Freedom of the Press in fighting gag orders.

Murphy said in response to several questions at his press conference that he did not want to talk about specific meetings with undercover FBI agents because he had not seen the videotapes of those meetings. He said he could "assure" reporters that none of the tapes showed him taking any money.

"In a business discussion it may have been brought up," Murphy said in answer to a question about money. But, he added, "I have been in violation of no law."

He said that no exact amount of money was ever discussed with him or other persons in his presence by the undercover agents, and that he would not further explain the conversations that ocurred until he had a chance to "review what is in the recordings."

According to sources familiar with the investigation, Murphy met last October with undercover agents at the Hilton Inn at Kennedy Airport in New York with Philadelphia attorney Howard Criden. At the meeting, which was taped, the men reportedly discussed how a "client" of the undercover agents could get into this country.

Murphy allegedly suggested that the man buy a house or a company to make it easier and at the end of the conversation, a closed briefcase filled with $50,000 was said to have been offered to the congressman. According to sources, Murphy said, "Howard will take that." Yesterday Murphy said "Nothing like that" occurred.

The Long Island newspaper Newsday reported that this meeting also discussed a deal involving the shipping industry in which one of the FBI agents -- posing as a sheik -- might be interested and Murphy said he would get back to them.

According to the Newsday account, Murphy was to get a hidden share in the proposed business arrangement and was taped in a meeting at the undercover operation's Washington house in which the deal was further discussed. No money was said to have passed hands during that conversation.

Murphy said in a statement last week he had been approached "by some person on behalf of Middle East interests" but "a routine background check disclosed to me that these persons were fraudulent" so he quit talking to them.

At his press conference, Murphy reiterated that neither he nor his attorney, Michael E. Tigar, has been informed of any specific allegations or charges.

If his requests for access to the tapes is denied Murphy added, he intends to sue the Justice Department for their release. In addition, he added, he and his lawyers "are investigating the possibility of filing a civil rights lawsuit against the federal government on the grounds that the massive leaks of information from federal agencies has created an atmosphere of hysteria."

He said the leaks will "obstruct the ability of any grand jury to give fair consideration of any case in which I might be involved."

Murphy released a series of letters written to Justice and FBI officials by Tigar outlining the same concerns about leaks and requests for information. Tigar said access to the tapes was necessary at this point as Murphy "may have the opportunity in this election year to rebut unwarranted charges and innuendos."

In another letter to Assistant Attorney General Phillip Heymann, Tigar asked that Justice Department strike force attorney Thomas Puccio of New York -- the supervising attorney in the Abscam cases -- be taken off Murphy's case because "he has been in regular contact with journalists with a political and personal motivation to discredit the congressman."

Murphy noted yesterday that one newspaper, the SoHo Weekly News in New York, had described Puccio and New York FBI head Neil Welch as the prime sources of leaks to the news media about Abscam.

Welch was quoted later as saying that charges that he was the source of leaks was "simply untrue." Puccio could not be reached for comment.

In Philadelphia, meanwhile, two other Democratic congressmen allegedly implicated in Abscam have filed for reelection, according to state records released yesterday and both face large numbers of opponents who have also filed as Democrats.

The two, Reps. Michael J. (Ozzie) Myers and Raymond F. Lederer, disregarded strong pleas by the Philadelphia Democratic leaderships that they not seek reelection. Nine other Democrats have filed to run against Lederer, and Myers faces 17 challengers.

The third Democratic representative from Pennsylvania implicated in Abscam, John T. Murtha of the western part of the state, has also filed for reelection but faces no Democratic primary opponents.

In Louisiana, the New Orleans Times-Picayune reported that the state's commissioner of administration, Charles E. Roemer II, took $15,000 in cash from an FBI informant last fall in an undercover operation involving the award of state and local insurance contracts.

The newspaper quoted sources as saying that Roemer described the payment as a "contribution" to the gubernatorial campaign of a state senator Roemer was backing, but there was no indication of the payment in the senator's campaign-financing reports.

A close ally of outgoing Gov. Edwin Edwards, Roemer had "no comment" when reporters in Baton Rouge asked whether he had taken the $15,000. The payment was reportedly made in a Baton Rouge hotel by Joseph Hauser, a twice-convicted insurance schemer working for the FBI, in the company of two other men, evidently FBI undercover agents.