The United Steelworkers yesterday overwhelmingly adopted complex new rules designed to prohibit outside contributions to union election campaigns, despite charges by opponents that the regulations would virtually assure the election of incumbents or their handpicked successors.

The rules were adopted in the wake of a bitter election fight last year for the presidency between former Chicago district director Edward Sadlowski and current president Lloyd McBride.

Sadlowski received large contributions from outside the union, including some from corporations and political activists. McBride has charged that those outside contributions would have made the union "beholden to outside interests" had Sadlowski won. McBride played a large role in drafting the new rules.

Those rules, which are expected to be challenged in court before the next election for the union's presidency in 1981, require a candidate or potential candidate, among other things, to keep a record of all contributions bigger than $5. They also prohibit a candidate from selling even a $5 raffle ticket to a non-steelworker and prohibit all contributions - direct or indirect - from even relatives of the candidate.

The rules apply to election for the five top international officers and the 25 district directors.

Opponents of the rules - perhaps 10 percent of the 3,900 delegates to the union's biennial convention here - said the new regulations strongly favor incumbents who can rely on the union's highly paid, headquarters staff as a ready source of large contributions. The new rules set no limits on the size of any individual contribution.

Although the district directors are elected, their staff members are appointed from headquarters. There are about 900 staff members in the field, and another 500 in Pittsburgh headquarters. Members of the union's executive board - the five officers and the 25 directors - did not see a written copy of the rules and the constitutional amendement they implement until yesterday morning, although the documents were read to them at a Tuesday breakfast.

About a quarter of the board members, who must pass an all resolutions sent to the floor, opposed the rules at the breakfast meeting, those who attended said.

James Balanoff, Sadlowski's successor as Chicago district director, opposed the rules and instead backed a special dues checkoff to fund a campaign chest to be equally spread among all candidates. Balanoff said that method would insure outside influences were kept out of the union while at the same time all candidates would be given an equal chance.

To be nominated for president, a candidate needs the endorsement of about 10 percent of the union's 5,500 locals. Balanoff, one of the union's leading dissidents, was roundly booed at the convention.

McBride told reporters Sunday that he would consider such a dues checkoff proposal. However, in his address at the end of a brief, but heated debate on the topic, McBriade made no mention of the alternate proposal. Instaed, he merely stressed the need to keep union officials responsible to no one else but union members.

Linus Wampler, district director from the region that includes the Minnesota iron ore mines, protested that the new rules would make it easy to "frame" a potential candidate because of the complex and burdensome reporting requirements, as well as the stiff restrictions on any form of outside contributions.

The rules will be enforced by a three-member oversight board composed of three as yet unnamed "prominent" non-steelworkers.