A U.S. corporate bid to buy into Britain's Westland Helicopters Ltd. failed today to get the required 75 percent of stockholders' votes necessary to implement the proposal.

In what was almost a sideline to the ongoing political controversy surrounding the business deal, only 67.2 percent of voting Westland stockholders approved the bid made by United Technologies' Sikorsky Aircraft division. Those who voted against it were presumed to favor a rival bid made by a consortium of five European companies, which was not put to a vote.

In a statement directed to the European bidders, Westland director Sir John Cuckney said the only "honorable" thing for them to do now was to withdraw so that Westland could be saved from bankruptcy.

Cuckney and the Westland board strongly favor the Sikorsky proposal. He indicated that Sikorsky may now revise its offer to terms that would be less advantageous to Westland but would require only 50 percent approval under British law.

The percentage of stockholders voting in favor of the Sikorsky proposal to take over 29.9 percent of Westland was much lower than had been predicted. Although Westland and Sikorsky had anticipated the possibility of failure, they expected the margin to be much slimmer.

They attributed the surprising outcome to the political upheaval over the past week, including the resignation of British Defense Secretary Michael Heseltine. Heseltine, who supports the European bid on the grounds that it is better for Britain's long-term defense interests, charged that Prime Minister Margaret Thatcher had engaged in behind-the-scenes maneuvering in favor of Sikorsky.

A second Thatcher Cabinet member, Secretary of Trade and Industry Leon Brittan, was nearly forced to resign early this week when the chief executive of British Aerospace, part of the European consortium, charged that Brittan had accused the company of acting "against the national interest" and told it to withdraw from the consortium.

Brittan denied making the accusation, and a major debate over who was telling the truth ensued in the House of Commons last Wednesday.

But today British Aerospace Chief Executive Sir Raymond Lygo released a letter he wrote to Brittan yesterday in which he acknowledged that there may have been an "unfortunate misunderstanding."

Opposition spokesmen, and even some Conservatives, interpreted Lygo's letter primarily as an effort to smooth things over. "Sir Raymond was put in a difficult position," said one Conservative member of Parliament. "After all, British Aerospace is a major government defense contractor."