The president said the move "paves the way for long-overdue progress in our nation's pursuit of equality," though he acknowledged "this is only one step."
"Hundreds of Fortune 500 companies already offer such benefits not only because it's the right thing to do, but because they recognize that it helps them compete for and retain the best possible talent -- and we need top talent serving their country right now more than ever," he said.
The president also announced his support for the Domestic Partners Benefits and Obligations Act, which he described as "crucial legislation that will guarantee these rights for all federal employees."
The remarks marked Mr. Obama's first significant comments on gay rights issues as president. While he heralded the move as an "historic step," many gay rights advocates have dismissed it as a minor action that only affects a small number of people and is designed to quell outrage over the president's lack of action on a number of issues important to the gay community.
They noted that health insurance benefits will still not be extended to gay partners and questioned whether the announcement has any real impact, since many of the benefits announced Wednesday have been available to some partners of gay federal employees since the Clinton administration.
Office of Personnel Management director John Berry addressed criticisms of the move in a conference call with reporters Wednesday afternoon, saying the president's announcement means Mr. Obama is "conferring a mandatory right" that was previously "subject to the whim of a supervisor."
A White House fact sheet said the memorandum means that domestic partners of federal civil service employees can be added to the long-term care insurance program and that supervisors can allow employees to use sick leave to care for domestic partners and "non-biological, non-adopted" children.
Benefits extended to same-sex partners of Foreign Service employees include "the use of medical facilities at posts abroad, medical evacuation from posts abroad, and inclusion in family size for housing allocations," according to the fact sheet.
The memorandum, which follows a review of current policy by Berry and Secretary Of State Hillary Clinton, also specifies that sexual orientation cannot be the basis for discrimination against federal workers in hiring decisions or promotions.
As a presidential candidate, Mr. Obama promised to "fight hard" for gay rights and repeal both the "don't ask, don't tell" policy that prohibits gays from serving openly in the military and the Defense Of Marriage Act that mandates:
But wary of a fight that could derail its ambitious agenda, the Obama administration has made no serious efforts to repeal "don't ask" and defended DOMA in a brief that compared same-sex marriage to "marriage of uncle to niece."
The brief prompted an outraged letter from Joe Solmonese, the president of the establishment gay rights group The Human Rights Campaign, and anger from many others in the gay rights community. A number of gay donors withdrew from a fundraiser for the Democratic National Committee next week featuring a speech by Vice President Joe Biden.
The president reaffirmed his opposition to DOMA Wednesday, calling it "discriminatory," and vowing to "work with Congress to overturn it."
In the conference call Wednesday, Berry, the highest-ranking openly gay official in the administration, said the president's announcement "is not in response, in any way, to any outside pressure." He said the process that culminated in the announcement had been "underway for many months" and that the White House's first priority on gay issues is "to get our house in order."
But the New York Times reported Wednesday that "administration officials said the timing of the announcement was intended to help contain the growing furor among gay rights groups."
Defenders of the administration say moving forward with the president's agenda on gay rights takes time, as well as legislation from Congress. (The president said Wednesday that "under current law we cannot provide same-sex couples with the full range of benefits enjoyed by heterosexual married couples.") They point to the fact that the State Department has promised to give same-sex partners of diplomats certain benefits as evidence that the White House is taking incremental steps.
But gay rights groups, who enthusiastically backed Mr. Obama during his presidential campaign, became disillusioned with the president even before he took office, thanks to his selection of pastor Rick Warren to deliver the invocation at his inauguration.
Conscious of the political capital lost by President Bill Clinton when he took on gays in the military early in his administration, they showed patience in the early days of Mr. Obama's presidency. But that patience has increasingly worn thin as the president has declined to implement his major campaign promises.
In addition, while the president said during the campaign that he supports civil unions but not gay marriage, that position has become less acceptable to gay rights advocates as states have begun legalizing gay marriage.
"They're talking about hate-crimes legislation and 'don't ask, don't tell' while people are getting married in Iowa," gay Democratic strategist Steve Elmendorf told the Los Angeles Times. "It seems on this subject the politicians are a little bit behind where the American people are."
The president Wednesday acknowledged that "we've got more work to do to ensure that government treats all its citizens equally; to fight injustice and intolerance in all its forms; and to bring about that more perfect union."
"I'm committed to these efforts, and I pledge to work tirelessly on behalf of these issues in the months and years to come," he said.