WASHINGTON — President Obama disappointed and vexed gay supporters on Wednesday with his decision, conveyed to activists by a senior adviser, not to sign an executive order banning discrimination by employers with federal contracts.

The executive order, which activists said had support from the Labor and Justice Departments, would have applied to gay, bisexual and transgender people working for or seeking employment from federal contractors. Current law does not protect against discrimination based on sexual orientation or gender identity, and legislation to do so, which Mr. Obama endorses, lacks sufficient votes in Congress.

“While it is not our usual practice to discuss executive orders that may or may not be under consideration, we do not expect that an executive order on L.G.B.T. nondiscrimination for federal contractors will be issued at this time,” said an administration official who would speak about the controversy only if provided anonymity. “We support legislation that has been introduced and we will continue to work with Congressional sponsors to build support for it.”

That stance departs from the White House’s prominent “we can’t wait” campaign: Since last fall, Mr. Obama has signed executive orders on a variety of issues, arguing that “we can’t wait” for legislation that Republicans in Congress refuse to let pass.