The nation’s Big Three automakers announced yesterday they will offer full health benefits to the same-sex domestic partners of their nearly 500,000 U.S. employees, a move hailed by gay-rights activists as a potential tipping point in persuading other old-economy employers to do the same.

Ford Motor Co., General Motors Corp. and DaimlerChrysler Corp. jointly announced that starting
Aug. 1, they will offer the benefits to the domestic partners of all employees who had shared a  “committed relationship for no less than six months.” The benefits are not being offered to un-married heterosexual couples.

Industry sources predicted that major foreign car makers with operations in the United States would soon follow.

Monica Emerson, director of diversity for DaimlerChrysler, said offering the new benefits, aside from being “the right thing to do,” was an effort to attract the best workers. “We really don’t know whether anyone has ever decided not to join us because of the lack of benefits, but clearly by taking this position we wont be taking that risk,” she said.

Emerson said “all corporations who want to be competitive will find themselves forced to cast wider nets to attract the best and the brightest.”

David Murphy, vice president of human resources at Ford, said the new benefit was saying to prospective employees, “Look, we are a diverse company and we do recognize not only race and gender but sexual orientation.” He said Ford was sending a recruiting signal to the labor force.

Ford estimates its additional cost of the new benefit at less than $5 million a year. Ford’s annual health care budget is $2.4 billion.

Although a number of major corporations including Lotus Corp., Microsoft Corp., The Walt Disney Co. and IBM already offer domestic partner health benefits, the announcement by the three automakers is the first time the major players in a single industry jointly took such action.

“There’s really nothing comparable,” said Kim Mills, educational director of the Human Rights Campaign, a gay-rights group that has been pressing the health care issue. “We’ve never seen an entire industry announce domestic partner benefits on the same day.”

Major airlines such as United, American and US Airways have also adopted same-sex benefit policies. But Mills said the action by the auto companies “will be an enormous boost. The auto industry is not viewed as socially progressive when it comes to employment policy,” she said.

The three automakers agreed to study the benefit idea as part of their contract agreement last year with the United Auto Workers union, which had proposed that each company set up a joint labor-management committee to study the economic feasibility. Yesterday’s announcement was the result of the committee efforts.

A UAW spokesman said the new benefits ‘were in keeping with the union’s history of negotiating new benefits for the American work force. “Here’s the heart of the old economy industry and we’re doing it,” he said.

The benefits will cover 100,000 blue and white collar workers at DaimlerChrysler, 159,000 at Ford and 204,000 at General Motors.

Murphy said Ford had considered whether the move would create a backlash from employees or customers. “We decided the business case for moving ahead was a strong one,” he said.