Backers of insurgent Edward Sadlowski considered challenging the United Steelworkers election yesterday as the apparent new president, establishment-backed Lloyd McBrid, claimed victory.

Aides to the 38-year-old union rebel said Sadlowski had not decided whether to contest the election and would not do so until the outcome is clear. They said their own latest count showed Sadlowski slightly ahead.

Independent tallies by the Associated Press and United Press International gave McBride a substantial leas as counting continued from Tuesday's voting in the 1.4 million-member union.

McBride, claiming a 75,000-vote lead out of more than 500,000 votes cast, issued a statement that was conciliatory toward Sadlowski's campaign as "irrational" and "ridiclous."

According to UPI, McBride, who was the candidate of the union's official heirarchy to succedd retiring president I.W. Abel, told a press conference in St. Louis: "It's evident he [Sadlowski] is irrational. He's fumbling and trying to discredit the union . . . Some of the things Sadlowski said were ridiclous.He has the habit of getting his mouth started about five minutes before his brain is in gear."

McBride said he wanted to "work in harmony with all steelworkers" and "wipe away any scars of factional fights" but added that "Sadlowski never could be a part of my team."

In Washington, Joseph L. Rauh, Sadlowski's attorney, said the voting invloved "violations serious enough so that a challenge should be considered and weighed against the margin."

Under union rules, challenges can be filed within 70 days of the election with the union's international headquarters in Pittsburgh and decisions can be appealed to the Labor Department and ultimately the courts.

Sadlowski aides in Chicago said reports of voting irregularities include charges of ballot box stuffing at a Birmingham, Ala., polling place and violations of secret ballot guarantees , campaigning at polling places and failure to require identification at various locations.

However, a Steelworkers attorney, Michael Gottesman, said only two minor irregularities involving 59 votes have been reported so far from the union's more than 5,300 locals in the United States and Canada.

An official at the Labor Department, which stationed advisers at the union's district offices, said complaints did not appear to be widespread.

A legal challenge could complicate steel industry contract negotiations that are scheduled to start Monday, but no delay or disruption was anticipated yesterday.