DES MOINES — It was a memorable political ad: Gov. Scott Walker of Wisconsin spoke directly into the camera in a 30-second spot last fall and called abortion an “agonizing” decision. He described himself as pro-life but, borrowing the language of the abortion rights movement, pointed to legislation he signed that leaves “the final decision to a woman and her doctor.”

That language was gone when Mr. Walker met privately with Iowa Republicans in a hotel conference room last month, according to a person who attended the meeting. There, he highlighted his early support for a “personhood amendment,” which defines life as beginning at conception and would effectively prohibit all abortions and some methods of birth control.

Mr. Walker has quickly vaulted into the top tier of likely Republican candidates in the presidential race, surging on the reputation he earned by taking on labor unions and surviving a bitter recall election in a swing state.

But the governor is also making an aggressive effort to win the hearts of the party’s Christian conservatives. In doing so, he is stressing a much harder line on social issues than he did just a few months ago, when he faced a robust challenge from a well-funded Democratic woman in his run for re-election as governor.