Updated 2:59 p.m. ET

Newt Gingrich affirmed his support for a constitutional amendment banning same-sex marriage in a detailed response to a marriage pledge by a conservative Iowa group.

Gingrich, who is currently leading national polls for the GOP presidential nomination, also told the Family Leader that he would sign an executive order restating that federal funds should not be used to pay for abortions overseas and defend the First Amendment right to religious liberty.

He also told the Family Leader that he would "vigorously enforce" the Defense of Marriage Act, which bans federal recognition of same-sex marriage. President Obama earlier this year instructed the Justice Department to stop defending the constitutionality of the law.

Earlier this year, Gingrich had declined to sign the Iowa group's marriage pledge because of concerns over wording. He had indicated he would do so if the group agreed to some changes.

The Family Leader has said it will make an endorsement in the presidential race, and has narrowed its list to Gingrich, Rick Perry, Michele Bachmann and Rick Santorum. Perry, Bachmann and Santorum have signed the pledge.

"We are pleased that Speaker Gingrich has affirmed our pledge and are thankful we have on record his statements," said Bob Vander Plaats of the Family Leader.

In addition to opposition to same-sex marriage, the 14-point pledge also asks candidates to vow "personal fidelity" to their spouse, appoint federal judges who are "faithful constitutionalists" and reject Islamic sharia law.

Gingrich, who has admitted past marital infidelity, made the following pledge about his own marriage:

I also pledge to uphold the institution of marriage through personal fidelity to my spouse and respect for the marital bonds of others.

Gingrich's opposition to gay marriage disappoints his lesbian half-sister, Candace Gingrich-Jones, a gay rights activist. The two recently saw each other, she told ABC News, and their encounter was "cordial."