"Relationship equality is a civil right, I believe that," he said. "The legal issue, the issue for policymakers is should we treat people the same? And I believe we should. There should be a license that would entitle a committed couple to have the same rights as a married couple. Again, I think the labels actually get in the way of the issue.

"What you call it and how you label it and how you describe it is not unimportant, it is important. But I think the most important issue, really, is the issue of legal equality, relationship equality," he said.

Kaine is a strict Catholic who is running in a swing state. He has taken similar stances, that legal and religious views should be kept separate, on other social issues including abortion — he reiterated at the breakfast that he is personally against abortion but that "government ought not to make people's moral decisions for them."

A number of Democrats have been forced to revisit gay marriage in the wake of Vice President Biden's comments on Sunday that he supported gay marriage. President Obama has said he's "evolving" on the issue and a spokesman did not say Monday whether he supported gay marriage or still opposed it in favor of civil unions.

Kaine, the chairman of the Democratic National Committee under Obama, said the renewed debate over gay marriage could cut both ways politically for Democrats but that it was a good debate to have.

"It can be politically positive in some areas and politically negative in others. I just think it's a good issue to have on the table ... because it's a sign of our progress that we are talking about this and thinking about it in different ways," he said.

Kaine, the first governor outside of Illinois to back Obama's presidential campaign, said he was "the president's friend" and a supporter, but pointed out areas where they disagreed, including dinging the president on the proposed "Buffett Rule," which would raise taxes on high-income earners. After saying he supported the law, he criticized the timing of its introduction.

"To me it seemed like stumbling over dollars to pick up pennies to be debating about the Buffett Rule," he said, arguing that Congress should focus on larger-scale deficit reduction and whether to renew the Bush-era tax cuts that will expire next January.

A Washington Post poll released Tuesday had Kaine tied with former Sen. George Allen (R-Va.) at 46 percent apiece, while Obama held a seven-point lead over Mitt Romney in the same poll. Other recent polls have shown Obama in better shape than Kaine as well. He said that he thinks the presidential race is "a bit closer" than the polls have indicated, and predicted close races for both himself and Obama in the state.

"I've never lost a race, but 53 percent is my North Star," he joked. "I'm the barely likable guy."

This post was updated at 11:11 a.m.