While Mr. Robertson did not mention Mr. Giuliani’s support of abortion rights, he said approvingly that Mr. Giuliani has “has assured the American people that his choices for judicial appointments will be men and women who share the judicial philosophy of John Roberts and Antonin Scalia,” who have argued against Roe v. Wade.

The endorsement comes just a month after a coalition of other prominent Christian conservatives threatened to back a third-party candidate if Mr. Giuliani were to become the Republican Party’s presidential nominee. Winning the support of Mr. Roberston could not only help Mr. Giuliani present himself as a viable candidate to the Christian right, but could also help him improve his standing in Iowa: Mr. Roberston finished second in the Iowa caucuses during his own run for president in 1988.

And the announcement threatened to overshadow an important conservative endorsement being announced by Senator John McCain of Arizona — the backing of Senator Sam Brownback of Kansas, who recently ended his own bid for president. While Mr. McCain opposes abortion rights, he has sometimes been viewed with suspicion by anti-abortion groups who felt muzzled by the McCain-Feingold campaign finance law that he helped pass. So the endorsement by Mr. Brownback, a staunch social conservative, was seen as an important achievement by the McCain campaign.

If Mr. Roberston’s influence within the Christian conservative movement has waned in recent years — he no longer attends the big strategy meetings of the new leaders who have sprung up — he still has clout as the chairman of a television station and the host of a television show, the 700 Club, that could boost Mr. Giuliani’s standing.

In an interview on the Christian Broadcasting Network in September, Mr. Giuliani, discussed his religious views in more detail than he often does on the trail.

“I believe in God, I pray to God, pray to Jesus for guidance and for help,” Mr. Giuliani said. “I have very, very strong views on religion that come about from having wanted to be a priest when I was younger and having studied theology for four years in college, it’s an area that I know really, really well academically. I understand the history of religion. Man and women’s relationship to God is one of the strongest, if not the strongest motivating thing in human history.”

And Mr. Giuliani had appealed directly to Mr. Robertson for support, and gave a speech at the university he founded, Regent University, over the summer. (Mitt Romney, who has also been courting religious conservatives, spoke at Regent as well.)

In his endorsement, which was announced in Washington, D.C., Mr. Roberston framed the biggest issue facing the nation as the threat of Islamic terrorists; the Giuliani campaign has been hoping that Mr. Giuliani’s tough stance on terrorism would outweigh traditional social issues for conservatives in the post-Sept. 11 world.