WASHINGTON (CNN) -- President Obama signed an executive order granting some benefits to same-sex partners of federal employees Wednesday, calling it "a historic step" but promising more action to come.

President Obama has been criticized by gay rights activists for not doing more since taking office.

"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," Obama said.

The signing followed sharp criticism of the president over a Justice Department motion filed last week in support of the Defense of Marriage Act -- which effectively bars the federal government from recognizing same-sex unions. Obama said he still wants to repeal the act.

"I believe it's discriminatory. I think it interferes with state's rights, and we will work with Congress to overturn it," he said.

The memorandum he signed Wednesday means same-sex partners of civil service employees can be added to the long-term care program, employees can use their sick leave to take care of domestic partners and children and same-sex partners of Foreign Service employees will be included in medical evacuations and housing allocations, according to the White House.

But it does not grant full health-care coverage, which would require an act of Congress, White House spokesman Robert Gibbs said.

As details of the impending memorandum began to filter out Wednesday, the reaction of some gay rights activists was not enthusiastic.

"I have to say, as a federal employee, I'm really disappointed," Lisa Polyak, 48, of Baltimore, Maryland, said of Obama's expected memorandum.

Polyak, who has worked for the federal government for more than two decades, is with the Army Medical Department. She was among the two dozen authors of the Dallas Principles, a set of eight statements that seek to guide the lesbian, gay, bisexual and transgender community toward "full civil equality," according to the document's preamble. Watch CNN's Paul Steinhauser discuss Obama's intent on benefits to same-sex partners »

"The benefits that the president might be announcing are already available," said Polyak, who has a partner and two children. "This isn't new. This isn't different."

She said federal employees are able to take sick leave for "anyone that was the close approximation of family" and said the long-term-care option has been available for people under the same category. Polyak said not having health insurance from the federal government for her partner of 27 years costs her family $4,000 to $5,000 a year, not including co-pays or deductibles.

Asked in a conference call with reporters whether these benefits were already available to same-sex partners of federal employees, Berry said such benefits are "subject to the whim of a supervisor."

"If you have an enlightened supervisor, yes, that is a possibility (that they have been available)," he said.

"What the president is doing today is making this no longer optional. He is making it mandatory. And he's making it clear that this is now the policy of the federal government."

Polyak disagreed, saying, "The idea that this was a fly-by-night [is] ... not true. I used it routinely."

She added, "It was guidance that everyone took advantage of and continues to take advantage at this moment."

Gay and lesbian advocates have also faulted the Obama administration for not moving to repeal the military's "Don't Ask, Don't Tell" policy that bars officials from asking about a service member's sexual orientation but also bars the service member from revealing it, and allows the dismissal of a service member if a same-sax orientation is discovered.

"There's so little we can say until we know what it is," said Carisa Cunningham, a spokeswoman for Gay & Lesbian Advocates & Defenders, a legal advocacy group that is challenging Section 3 of the Defense of Marriage Act in federal court in Massachusetts.

Section 3 prevents the federal government from giving Social Security and other protections to same-sex married couples.

"Laws have to change ... and in particular, the Defense of Marriage Act needs to change, so whatever the few benefits that the president as an employer can grant, there won't be a lot of them," Cunningham said.

President Bill Clinton signed the Defense of Marriage Act into law in 1996.

Obama rankled gay advocates in January when he selected mega-church pastor Rick Warren to deliver the invocation at his inauguration. Warren, in an interview with Beliefnet, likened homosexuality to bestiality and incest. He also supported California's Proposition 8, which banned same-sex marriage in that state.

During the Warren controversy, Obama -- who frequently spoke out in favor of gay and lesbian rights during the campaign but has said he opposes same-sex marriage -- declared himself "a fierce advocate for gay and lesbian Americans."

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