After years of sending in their regrets, Republicans are RSVPing yes to gay causes more than ever.

Prominent GOP lobbyists, activists and Members of Congress will attend or lend their names to two big gay rights events tonight, including one co-hosted by Ken Mehlman, the former Republican National Committee chairman and George W. Bush campaign manager who recently announced he was gay.

In his first gay rights political event since going public with his sexual orientation, Mehlman is hosting a fundraiser for the American Foundation for Equal Rights, which is spearheading the court battle for gay marriage.

The cocktail reception in New York City also features Ted Olson, one of the two lawyers who successfully argued the case before a federal judge in California to overturn the state’s ban on gay marriage. Olson was solicitor general under Bush.

The fundraiser has also drawn a bipartisan host list that includes Mary Cheney — the openly gay daughter of former Vice President Dick Cheney — and Steve Schmidt, a senior presidential campaign adviser to Sen. John McCain (R-Ariz.).

The list also has several high-level Republican lobbyists, including AT&T’s Jim Cicconi and former staffers to one-time Bush political adviser Karl Rove, who encouraged a state anti-gay-marriage referendum in 2004 to drive up conservative turnout in the presidential race.

At the same time as the New York event, the Log Cabin Republicans, a gay rights group, will hold its national dinner in Washington, D.C. Among those attending the Log Cabin dinner or cocktail reception at the Capitol Hill Club are the anti-tax activist Grover Norquist and Sen. John Cornyn (Texas), chairman of the National Republican Senatorial Committee. National Republican Congressional Committee Chairman Pete Sessions (Texas) had been scheduled to attend the Log Cabin dinner but is now not expected because of a House Republican caucus meeting that evening.

To some observers, tonight’s events are indicative of a growing change in attitude among at least some in the Republican Party who for years were wary of having their names attached to gay rights events, fearing that it would alienate the party’s base.

“There is a general cultural shift,” said R. Clarke Cooper, the executive director of the Log Cabin Republicans, who worked in the Bush administration. “Being conservative and gay are not mutually exclusive.”

The participation by Republicans in these events, however, does not signal a wholesale change in party stands on gay issues. GOP Senators were key to blocking a defense bill Tuesday that included a repeal of the military’s “don’t ask, don’t tell” policy.

In voting to oppose opening debate on the military bill, Cornyn suggested Democratic leaders were trying to score election-year points with gay rights and other liberal groups. But the Texas Republican has also refused to accede to a demand by Tony Perkins, the president of the socially conservative Family Research Council, to withdraw from tonight’s Log Cabin reception.

Last week, Perkins wrote to the Texas Senator that the Log Cabin Republicans had been instrumental in pushing legal challenges to bans on gay marriage and added that “it is deeply troubling to me that you would lend your credibility to this organization.”

Cornyn wrote back saying that while he disagreed with the gay rights group on some issues, he would still attend the Log Cabin reception, which is a fundraiser for the organization’s political action committee.

“First, part of my job is to reach out to those committed to defeat Senate Democrats this November,” Cornyn wrote. “Second, as social conservatives we affirm the basic dignity of every human life, including not only unborn children, but also adults with whom we may disagree. I believe we are all made in the image and likeness of God.”

Although Cornyn’s appearance at the Log Cabin event is noteworthy, tonight’s events mark Mehlman’s debut in the gay-rights arena, said Cooper, who added that the former GOP official would also be speaking by video to the Log Cabin dinner, even though Mehlman will actually be at the American Foundation for Equal Rights dinner in New York.

When he came out last month, Mehlman said he would fundraise to help the legal challenge to Proposition 8, the California measure banning gay marriage.

With tickets going for $5,000 a person and $10,000 a couple, the American Foundation for Equal Rights cocktail reception at New York’s Mandarin Oriental Hotel has a star-studded host roster. It includes big-time GOP donor and hedge fund manager Paul E. Singer and Peter Thiel, the gay California venture capitalist who supported Rep. Ron Paul (R-Texas) for president in 2008.

Former New Jersey Gov. Christine Todd Whitman (R) and one-time Massachusetts Gov. William Weld (R), longtime gay rights supporters, are backing the effort.

Also on the list is Patton Boggs partner Benjamin Ginsberg, a former RNC counsel, and former Federal Election Commission Chairman Michael Toner, a Republican who is now an adviser with Bryan Cave Strategies.

Former Rep. Michael Huffington (R-Calif.), who is gay and the ex-husband of columnist and publisher Arianna Huffington, is also a host, as is former Bush communications adviser Nicolle Wallace and GOP consultant Tom Synhorst, who was an adviser to former Sen. Bob Dole (R-Kan.).

Other hosts include Israel Hernandez, a longtime aide to the Bush family; Mehlman Vogel Castagnetti lobbyist Bruce Mehlman, the brother of Ken Mehlman; and Margaret Hoover, who worked for the Bush campaign and is the great granddaughter of President Herbert Hoover. The event is being put together by Susan Ralston, who worked for Rove in the White House and for former lobbyist Jack Abramoff. The foundation’s president is Chad Griffin, a Democrat who worked with liberal Hollywood producer Rob Reiner.

Olson and Mehlman’s involvement, Griffin said, “has removed and lifted the partisan veil.”

Of course, Democrats aren’t ceding the gay rights platform to the GOP. Plenty of the majority party’s heavy hitters are sponsoring the New York City event, including John Podesta, who heads the liberal Center for American Progress; former House Majority Leader Dick Gephardt (D-Mo.); and lobbyist Steve Elmendorf, who worked for Gephardt on the Hill.