NEW YORK (Fortune) -- Most of America's best-known companies are reaching out to gay and lesbian workers, as well as gay consumers, despite the criticism they get from conservative Christian groups.

Consider: No Fortune 500 company offered health benefits to the domestic partners of gay and lesbian workers until Levi Strauss did so in 1992. Today, more than half of the Fortune 500 offer those benefits.

Beyond that, blue-chip companies recruit gay MBAs. They seek out suppliers owned by gay and lesbian business people. And they advertise in gay media such as Logo, the cable TV network launched last year by Viacom. (Charts)

The latest evidence that corporate America is becoming more gay-friendly comes in the form of a new report on workplace practices released this week by the Human Rights Campaign (HRC), the nation's largest lesbian and gay political organization.

The report, called the Corporate Equality Index, gives 138 major U.S. companies a perfect 100 percent score when it comes to providing equal benefits to gay, lesbian, bisexual and transgender (GLBT) workers. That's 10 times as many as received a perfect score when the group did its first survey of workplace practices in 2002.

To get a perfect score, companies must explicitly ban discrimination based on sexual orientation, provide domestic partner benefits and offer diversity training. Beyond that, they must advertise to the gay community and contribute to GLBT community groups.

"These policies have become mainstream business practice," says Daryl Herrschaft, director of the Human Rights Campaign's workplace project and author of the 68-page report. "This is really a race to the top for corporations."

Companies with perfect scores for 2006 include automakers Ford (Charts), General Motors (Charts) and Daimler Chrysler (Charts), computer makers Apple (Charts), Dell (Charts) and Hewlett Packard, tech firms IBM, Intel and Microsoft, financial giants Citigroup, J.P. Morgan Chase and Merrill Lynch and consumer products companies Coca Cola, PepsiCo and Johnson & Johnson. Several aerospace and defense industry firms - Boeing, Northrop Grumman and Raytheon - also notched perfect scores.

"I'm so proud of my company," says Louise Young, a senior software engineer at Raytheon, a lesbian and a political activist for more than 30 years. "I've been a witness to great change, especially in corporate America."

Just three companies received a zero score from the Human Rights Campaign. They are oil giant Exxon Mobil (Charts), grocery chain Meijer Inc and tech firm Perot Systems.

Asked to respond, ExxonMobil spokesman Russ Roberts told Fortune by e-mail that the company has "written policies [that] prohibit discrimination or harassment for any reason, including sexual orientation." The company's health benefits in the U.S., he said, rely on the "definition of spouse used in federal legislation, which has the effect of limiting coverage to heterosexual couples." Meijer said it did not participate in the survey, and Perot Systems did not respond to a request for comment.

(Time Warner, parent company of Fortune and CNN, got a score of 85, behind its rivals Viacom and Walt Disney.)

Many companies are going beyond the workplace to appeal to GLBT audiences. Wal-Mart has joined the National Gay and Lesbian Chamber of Commerce and sponsored a panel at a conference of GLBT journalists. Kraft and Walgreen's were among dozens of sponsors of the Gay Games, an athletic competition that drew more than 12,000 participants to Chicago last summer. IBM helped organize GLBT engineers on college campuses.

Why the changes?

Herrschaft and several corporate executives who joined in the release of the Human Rights Campaign report say companies that want to to attract and motivate workers need a diverse workforce in which everyone can feel welcome.

Carmen Lewis, director of workforce diversity for AT&T, says: "It's critical that all employees be able to work in a discrimination-free and harassment-free environment, regardless of their differences."

Of course, there's been a backlash. The American Family Association, a conservative Christian group, has called for a boycott of Ford because it says the automaker promotes "the homosexual agenda." The Family Research Council accused Wal-Mart of "surrendering to the radical homosexual lobby." Sponsors of the Gay Games got thousands of negative e-mails.

Inside companies, too, there's debate. Might not pro-gay policies trouble employees who are conservative Christians or orthodox Jews?

Executives say that's possible, and that all employees are entitled to their private beliefs. But, they say, once people arrive at the office, they are obligated to treat colleagues with fairness and respect.

"There may always be someone who doesn't agree" with corporate diversity initiatives, says Maria Ferris, director of global workforce diversity at IBM. "But the fact that we all have to come to work and produce, and put that aside...is what makes us a great company."

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