Washington, DC (LifeNews.com) -- John McCain hasn't given much insight publicly about the person he will choose to become his vice-presidential running mate. But he told a television program on Tuesday night that he would have a "difficult" time picking someone who didn't have a pro-life view on abortion.

In an interview with Chris Matthews, the host of MSNBC's "Hardball" program, McCain responded to a question about a running mate with different abortion views than his.

"Would you put a person on the ticket with you -- like the former governor of this state who is very popular Tom Ridge -- even though he may disagree with you on the issue of Roe v. Wade and abortion rights? Would you put somebody on the ticket like that on that one issue. Would that stop him?" Matthews asked McCain."

"I don't know if it would stop him but it would be difficult," McCain said in response.

Matthews asked McCain if he had a pro-life litmus test on choosing a running mate.

"I'm not saying that would be necessarily," McCain said. (see video)

"But I am saying it's basically the respect and cherishing of the right of the unborn is one of the fundamental principles of my party and it's a deeply held belief of mine," the eventual GOP nominee added.

McCain spokesman Joseph Pounder followed up on the comments in an interview with CBN News.

"John McCain is opposed to any sort of a litmus test, just like past Republican presidential nominees," he said. "As John McCain has said repeatedly, his vice-presidential nominee will be someone who shares his principles, values and priorities."

CBN News correspondent David Brody talked about McCain's comments on his blog.

"You can tell that now that he is the nominee, he needs to be extra careful," he said. "His line yesterday in defense of the pro-life position was pretty strong."

Earlier this month, National Right to Life indicated it supports McCain because the contrast on abortion between him and the pro-abortion candidates Barack Obama and Hillary Clinton is too significant.

"National Right to Life supports Senator John McCain for election as President of the United States and strongly opposes both Barack Obama and Hillary Clinton and urges all pro-life citizens to do likewise," the group told LifeNews.com.

On abortion issues, McCain has a strongly pro-life voting record and has supported bills to ban partial-birth abortions, respect parental involvement regarding teenagers and prohibit tax-funded abortions in a variety of situations.

The Arizona senator has also repeatedly called for overturning Roe v. Wade, said he would appoint judges who won't legislate from the bench, and says he will keep the pro-life plank in the Republican Party platform.

Both Barack Obama and Hillary Clinton have 100 percent pro-abortion voting records with the group and have pledged to only appoint federal judges who will keep unlimited legal abortions in place for another 35 years.

Those differences are so significant and will affect so many lives of women and unborn children that NRLC officials told LifeNews.com supporting McCain made perfect sense.