Candidates vying for the Democratic party's presidential nomination stepped out one by one Thursday night to face tough questions devoted exclusively to gay and lesbian issues, with the frontrunners forced to account for their apparent reluctance to embrace same-sex marriage.

Barack Obama, the Illinois senator who was the first of six candidates to speak before the forum, defended his position that civil unions for gay couples were not a "lesser thing" than marriage, and brushed aside the issue as a matter of semantics.

"Semantics may be important to some," he said. "From my perspective, what I'm interested [in] is making sure that those legal rights are available to people."

Obama went on to say that he wished to see a situation in which civil unions of same-sex couples was a "widely recognized" concept. If people could achieve civil rights under the law, "then my sense is that's enormous progress," Obama said.

Obama is a member of the United Church of Christ, which supports gay marriage, but Obama has yet to go that far.

'Historic moment'

It's the first time U.S. presidential candidates took part in a debate devoted to such hot-button issues, including homosexuality in the armed forces, HIV/AIDS, hate crimes and same-sex marriage.

Obama called it a "historic moment … for America."

The two-hour debate was co-sponsored by the Human Rights Campaign, a civil rights organization working for gay rights, and Logo, a gay and lesbian cable network. Logo broadcast the debate live on television and the internet.

Human Rights Campaign president Joe Solmonese, singer Melissa Etheridge and Washington Post editorial writer Jonathan Capehart acted as debate panelists.

No frontrunner supporting same-sex marriage 

None of the frontrunners was calling for the legalization of same-sex marriage.

New Mexico Gov. Bill Richardson said the nation was on "a path to full inclusion" but added, "In my judgment, what is achievable is civil unions with full marriage rights."

The candidates appeared sequentially at 15-minute intervals seated in an upholstered chair, but never shared the stage with one another. About 200 invited guests comprised the audience.

All of the candidates:

• Support a federal ban on anti-gay job discrimination.
• Favour the repeal of a "don't ask, don't tell" policy that bars gays from serving openly in the military.
• Support civil unions that would extend marriage-like rights to same-sex couples.

Two candidates — Dennis Kucinich and Mike Gravel — have endorsed same-sex marriages, something a majority of Americans oppose. Both candidates are considered longshots for the nomination.

But frontrunners Obama, Hillary Rodham Clinton and John Edwards did not go that far.

Republicans 'use hate-mongering'

Clinton's adviser, Ethan Geto, said it is unlikely any viable contender for the nomination would support same-sex marriage in this election cycle. 

Clinton was cheered by the crowd when she alluded to the prospect for change at the White House in the 2008 election.

Edwards, a former North Carolina senator and failed vice-presidential candidate, argued that Democrats must speak out against discrimination coming from the other party.

"If you stand quietly by and let it happen, what happens is it takes hold," Edwards said. Without speaking out against intolerance it becomes "OK for the Republicans in their politics to divide America and use hate-mongering to separate us," he said.

Of the eight Democratic candidates, two did not attend — Senators Joe Biden of Delaware and Chris Dodd of Connecticut.

Logo general manager Lisa Sherman said the network offered a separate forum for Republican candidates, but none showed any interest in the idea.

With files from the Associated Press