Lou Rocco/ABC News

Just days after affirming his support for same-sex marriage, President Obama today declined to say whether he would go a step further and publicly take up the fight to repeal the Defense of Marriage Act .

While the administration has already stopped defending legal challenges to the legislation, which defines marriage as between a man and a woman, the president said the rest is up to Capitol Hill.

"Congress is clearly on notice that I think it's a bad idea," the president said in an interview on ABC's "The View."

The full interview airs on "The View" Tuesday on ABC at 11 a.m.

"This is going to be a big contrast in the campaign, because you've got Gov. Romney saying we should actually have a constitutional amendment installing the notion that you can't have same-sex marriages," Obama said.

When asked by ABC's Barbara Walters if he would fight federal laws that limit the rights of gay and lesbian couples, the president said, "We don't think the Defense of Marriage Act is constitutional."

"This is something that historically had been determined at the state level and part of my believing ultimately that civil unions weren't sufficient, and I've been a longtime supporter of civil unions for same-sex couples, was partly because of the issue of Social Security benefits and other laws," the president said.

Obama had long said he opposed same-sex marriage, but repeatedly qualified that by saying that his view was "evolving," as he delayed taking a firm stance on the social issue. But last week, in an interview with " Good Morning America's" Robin Roberts , the president declared he now believes same-sex couples should have the right to marry.

Obama was making his fourth appearance on "The View," and his second as president. Obama made history as the first sitting president to make an appearance on daytime television when he visited the women of "The View" in July 2010.

The full interview airs Tuesday on ABC.

Tune into "World News with Diane Sawyer" tonight for more from the interview.