The Environmental Protection Agency is preparing to hire private lawyers at a cost of up to $70,000 to help defend Administrator Anne M. Gorsuch against a contempt-of-Congress charge lodged last month by the House.

EPA officials said yesterday that they need the outside advice even though the Justice Department, not the EPA, is charged by law with representing Gorsuch and has assigned a team of lawyers to the historic case.

"This is not an indication that we have lost confidence in the Justice Department," said a senior EPA official. "We just very simply wanted to have available to us a kind of constitutional expertise that frankly we don't have here on our staff."

The official said the agency plans to sign a contract soon with two lawyers from the Boston firm of Ropes and Gray to act as consultants on constitutional and procedural issues in the case. The two men will advise EPA's lawyers, who in turn are conferring with Justice at each stage of the proceedings.

Justice Department officials declined to comment on their reaction to EPA's move except to say they had nothing to do with it. They also predicted that the outside advice would have little influence on their handling of the case.

"It's their [EPA's] money, and their choice in how they spend it," said a department official. "But I don't think it will have much effect on us."

The proceedings against Gorsuch mark the first time that the full House has charged a Cabinet-level official with contempt of Congress for refusing to comply with a subpoena.

Gorsuch, acting under orders from President Reagan, refused to turn over documents on her agency's prosecution of companies responsible for the nation's most dangerous hazardous waste dumps.

Several administration officials acknowledged that it is unusual for an agency to hire outside counsel while being represented by Justice, but one official added, "Everything that happens in this case is out of the ordinary."

However, House leaders were not so sanguine.

"I think it's somewhat outrageous," said Rep. Elliott H. Levitas (D-Ga.), chairman of the Public Works subcommittee that subpoenaed the documents. "Now they're going to spend taxpayers' money getting legal advice when the taxpayers are already paying millions of dollars to lawyers in the Justice Department and in EPA for the same advice.

"I also have a positive reaction, though," he added. "Maybe they'll finally get some good advice and realize that they should just give us the documents."

The unusual legal twists in the case began minutes after the House voted 259 to 105 last month to cite Gorsuch for contempt.

Justice Department officials were charged by law with prosecuting Gorsuch even though they had advised her to invoke executive privilege in withholding the documents.

However, Justice officials announced soon after the contempt vote that they would not prosecute Gorsuch.

Instead, they sued the House, charging that the contempt proceeding and the subpoena were unconstitutional--an intrusion on the authority of the executive branch to withhold sensitive information from Congress.

The House last week asked a judge to throw out the lawsuit, calling it "a misguided attempt to restrain the operation of the legislative process." The judge has not yet decided whether to hear the suit.

EPA and Justice have differed in the past on how to handle the case. EPA at first allowed a House panel to review many of its sensitive hazardous waste documents, but then changed course under advice from Justice.

"Justice may have an institutional bias against going outside because they feel they can handle this," said an EPA official. "But we want to know for ourselves: Is Mrs. Gorsuch shielded simply because she's following the president's orders?"

The Ropes and Gray attorneys who will handle the case are G. Marshall Moriarty and Thomas M. Susman, a former legislative director for Sen. Edward M. Kennedy (D-Mass.). Susman also was a staff member of the Senate Judiciary Committee during the 1973 Watergate investigation.

EPA officials said the men will be hired for the rest of the fiscal year at an hourly fee that is still under negotiation. They said the total cost is expected to be between $65,000 and $70,000.

The money will come from the agency's budget for general contracts to study air, water and hazardous waste issues, they said.

House lawyers also hired an outside consultant, Fordham University constitutional law professor Eugene Gressman, to assist them in the case. They said his bill would be less than $500.