The federal government already prohibits discrimination against gay men, lesbians and bisexuals in its own work force, but the order Mr. Obama signed on Monday would extend that to companies that do work for the federal government. It also for the first time explicitly protects federal workers based not just on sexual orientation but also on gender identity, meaning transgender employees….

The president’s order applies to only a fraction of those who would be affected by congressional legislation, but he has been under heavy pressure from a critical Democratic core constituency to take action on his own without waiting for lawmakers.

His order adds sexual orientation and gender identity to the list of categories protected among federal contractors that was first approved by President Lyndon B. Johnson in 1965. And it adds gender identity as a protected category to a 1969 directive by President Richard M. Nixon that applies to federal employees, which was later amended by President Bill Clinton to include sexual orientation.