Steve Schmidt, Arizona Senator John McCain's presidential campaign manager, is expected to endorse gay marriage today during a lunchtime speech to Log Cabin Republicans – a conservative gay group – at their annual convention.

Schmidt revealed his position on the issue last month in an interview with gay weekly The Washington Blade.

Schmidt, who has a sister who is a lesbian, is expected to endorse gay marriage, arguing it is a conservative issue.

“There is a sound conservative argument to be made for same-sex marriage,” Schmidt will say, according to speech excerpts published by CNN. “I believe conservatives, more than liberals, insist that rights come with responsibilities. No other exercise of one's liberty comes with greater responsibilities than marriage.”

Like Schmidt, Megan McCain, daughter of Senator McCain, is also a gay marriage supporter. She too is expected to participate in the convention over the weekend and is likely to urge the Republican Party to make its political tent more gay friendly.

“I am determined to build a more-inclusive GOP,” McCain recently wrote in an editorial titled Memo to the GOP: Go Gay at Tina Brown's online publication The Daily Beast. “If the Republican Party has any hope of gaining substantial support from a wider, younger base, we need to get past our anti-gay rhetoric.”

In his speech, Schmidt compares gay rights to civil rights, an idea gay marriage opponents reject.

“It cannot be argued that marriage between people of the same sex in un-American or threatens the rights of others,” he says in the speech. “On the contrary, it seems to me that denying two consenting adults of the same sex the right to form a lawful union that is protected and respected by the state denies them two of the most basic natural rights affirmed in the preamble of our Declaration of Independence – liberty, and the pursuit of happiness.”

“That, I believe, gives the argument of same sex marriage proponents its moral force,” Schmidt will say.

The four-day convention ends Sunday.