The Labor Department's investigation of the contested United Steel-workers election is a "sham," attorneys for union insurgent Edward Sadlowski charged yesterday in a formal protest to Labor Secretary Ray Marshall.

Sadlowski's lawyers, Joseph L. Rauh Jr. and Judith Schneider, accused Marshall of refusing to meet with them or to take steps necessary to determine whether the Feb. 8 election was conducted legally.

They objected particularly to the department's inquiries into the conduct of the Sadlowski forces, saying the investigators should be concentrating instead on the union's "official family" and the candidate it backed for the union presidency, Lloyd McBride.

McBride defeated Sadlowski by about 80,000 votes, according to the union's count, but Sadlowski has challenged the outcome, charging illegal electioneering, forced contributions and a "wholesale cover-up" by union leaders supporting McBride. Sadlowski asked for the Labor Department investigation on June 17 after the union rejected his complaints.

The department immediately announced it was deploying 250 investigators to check out the charges but rejected Sadlowski's request for detailed questionnaires to be answered under oath by about 18,000 union officials.

"The sad fact is that the department has no affirmative zeal for this investigation and, instead of improving on our suggestions, rejects them out of hand and without a hearing," said Rauh and Schneider, who contended that only questions answered under risk of perjury would produce the truth.

They said the Labor Department has always been lax in enforcing the law governing union elections and Marshall "dashed the remaining hope" that things would be different under the Carter administration. "Even the Nixon Secretary of Labor [George P. Schultz] did not refuse to receive representatives of the union reform movement," they said.

A Labor Department spokesman said the investigation is "continuing in a very professional manner" and asserted that departmental investigations have led to overturning numerous union elections. "If we reacted to every public statement Joe Rauh made, we wouldn't have time to do anything else," he said.