AUGUSTA — Two wealthy Democratic activists have pledged $100,000 to Mainers United for Marriage, kicking off a four-week matching gift challenge as part of an effort to pass a gay marriage ballot question in November.

Chris Hughes, a founder of Facebook, and his partner Sean Eldridge, president of Hudson River Ventures, are pledging the money, according to a statement released today by Mainers United.

“Voters in Maine have a historic opportunity to win marriage at the ballot in November,” Eldridge said.

“We are encouraged by strong statewide support for the initiative and the top-notch campaign team that’s in place, and we hope that our support will motivate others to invest in the campaign. With numerous marriage-equality cases heading to the Supreme Court, there is nothing more important than growing momentum and winning the freedom to marry in more states.”

Hughes, 28, left Facebook in 2007 with an estimated $700 million, and has helped raise funds for President Barack Obama and other high-powered Democrats, according to the New York Times. A feature story in the newspaper that ran May 6 showed Hughes Eldridge on their estate in New York and in their SoHo apartment.

The story described the couple as “a significant force in political circles, becoming enthusiastic fundraisers for the progressive issues they support, which include gay civil rights.”

Hughes now serves as publisher and editor in chief of The New Republic.

In 2009, when voters rejected gay marriage at the polls in Maine, groups on both sides of the issue spent a combined $9.6 million to influence voters. Both sides say they expect a similar amount this time around, with significant sums coming from out of state sources.

“This matching gift challenge is critical to raising the early resources we need for our campaign,” said Matt McTighe, campaign manager for Mainers United.

Last week, President Obama’s announcement that he now supports gay marriage boosted the hopes of supporters. But opponents pointed to a vote in North Carolina last week in support of a constitutional amendment to ban gay marriage, which passed with 61 percent support. They say Mainers haven’t changed their minds on the issue since it was rejected in 2009 by a 53-47 percent margin.

“The events in North Carolina are going to help significantly,” said Bob Emrich, campaign manager of the Protect Marriage Maine PAC, which is the leading opposition group. “It shows the momentum has not changed. People will see it as a worthwhile investment.”