As John McCain faces increasing pressure to select his vice presidential running mate, former Arkansas governor and one-time presidential candidate Mike Huckabee said Thursday values voters are watching closely for an abortion opponent.

Huckabee said the Arizona senator must choose someone he is "comfortable with" and hopes that person opposes abortion rights, a hot-button issues that could inflame some voters among the party's conservative base.

McCain told the Weekly Standard on Wednesday that he has not ruled out choosing Pennsylvania's popular former Gov. Tom Ridge as a running mate despite his support for abortion rights, a statement that has come under fire by some conservatives in recent days.

"I wish he were pro-life," Huckabee said of Ridge.

In his interview with the conservative publication, McCain said the pro-life position is "one of the important aspects or fundamentals of the Republican Party."

"And also I feel that -- and I'm not trying to equivocate here -- that Americans want us to work together," he said. "Tom Ridge is one of the great leaders and he happens to be pro-choice. And I don't think that that would necessarily would rule Tom Ridge out."

McCain, who is against abortion rights, appeared to be testing the issue -- weighing the benefits against the costs of picking Ridge, who could help the Arizona senator win Pennsylvania. The presidential election is won on a state-by-state basis with more populous states, such as Pennsylvania, carrying greater weight in the results.

Huckabee said that if McCain's vice presidential choice is "not hardcore pro-life," he asks that he or she "not do anything that would be disruptive to what has been very important to the Republican platform."

Huckabee also expressed opposition to the prospect of choosing former Massachusetts governor and presidential candidate Mitt Romney.

"I think a lot of people, not just social conservatives, but a lot of the Republicans I know are not necessarily comfortable with Romney," he said in an interview with CBS News. "But it has nothing to do with religion. It has everything to do with inconsistencies in positions he's held, and that's it."

Huckabee ruled out any possibility that he will be asked to join the GOP ticket.

"I have no expectations that I'm going to get that phone call," he told FOX News.

"My commitment is to support him. And I don't request that he support me in order to get my support," he added.

The Associated Press contributed to this report.