President Barack Obama will deliver the keynote address Saturday to a gathering of gay and lesbian activists, a key constituency that hasn’t always been receptive to the president’s policies and style of leadership.

Supporters say Obama’s accomplishments on gay rights issues have been substantial since he last headlined the annual National Dinner of the Human Rights Campaign, in 2009, including the repeal of the military’s “Don’t Ask, Don’t Tell” policy. However, his lack of support for gay marriage still stands out as a snub for many.

Obama currently supports same-sex civil unions, and has said his views on gay marriage are “evolving.” He recently announced his support of the Respect for Marriage Act, a bill that would repeal the Defense of Marriage Act, a 1996 law that defines marriage as between a man and a woman.

Organizations working actively to legalize same-sex marriage say they hope Obama eventually changes his stance

“I’d like to see the president bring his message of support for the freedom to marry to a broader audience, perhaps in a conversational setting, so that all Americans can hear him talk about why marriage matters to loving gay and lesbian couples and their families,” said Evan Wolfson, the founder and president of Freedom to Marry. “It is important that the president lay out the case for Americans opening their hearts to the values of fairness and treating others as they would want to be treated.”

Wolfson, along with other organizations advocating for legal same-sex marriages, said the Obama administration had made significant progress on some issues, but that support for marriage equality was still an important goal.

“We applaud the administration’s progress, while we also encourage him to ‘evolve faster’ on supporting full marriage equality,” Stuart Gaffney, media director for Marriage Equality USA, said Saturday. He said he wasn’t aware of any opposition within his organization to the HRC’s selection of Obama as their keynote speaker.

“We look forward to the day soon when our president stands with that pro-equality majority,” Gaffney added.

The Log Cabin Republicans, an organization that represents gay and lesbian conservatives, says Obama’s appearance Saturday night is more about politics than substantive policy change.

“President Obama’s appearance at the Human Rights Campaign Dinner this evening is more emblematic of their role as an ostensibly partisan organization than a representation of the gay and lesbian community,” said Christian Berle, the group’s deputy executive director.

Berle said Obama’s stance on gay marriage didn’t match that of most Americans.

“As all Americans are becoming open to marriage equality, the president is taking a retreat,” Berle said. “Instead he is turning to the gay community for money and applause.”

“If the president wants to deserve all the money and adulation he has already received from the gay community, he should announce his firm support for everyone’s freedom to marry,” Berle said.

Organizers of Saturday’s event said Obama’s record on gay rights issues is still strong, despite the lack of endorsement for marriage equality.

“This president has accomplished more in the last two years on behalf of LGBT Americans than was accomplished in the last 40 years,” HRC Vice President Fred Sainz said. “From the repeal of ‘Don’t Ask, Don’t Tell’ to dozens of policy directives, this president has made the lives of countless millions better and the Human Rights Campaign has endorsed the president’s re-election.”

Saturday’s event is expected to draw 3,000 gay activists, and will take place at a convention center in downtown Washington. The speech will be streamed live online.

A CNN/ORC International poll taken Sept. 9 to 11 showed 53 percent of Americans believe marriages between gay and lesbian couples should be considered valid. That number has steadily been rising in CNN/ORC International polls since 2008.

CNN’s Athena Jones contributed to this report.