WASHINGTON — On a January morning in 1980, a day when thousands of abortion opponents protested the anniversary of Roe v. Wade across from the White House, a group of conservative evangelical leaders sat down for breakfast with the born-again president, Jimmy Carter.

The responses they heard on abortion, the Equal Rights Amendment, gay rights and other social issues left them unimpressed. A relationship that already had been strained was irretrievably broken.

The next fall, white evangelicals, who four years earlier had supported the election of a Southern Baptist Sunday-school teacher, a man quite open about the central role of faith in his life, instead voted overwhelmingly for his defeat, switching their loyalties to former President Reagan and the Republican Party.

Now, with the retirement of Justice Sandra Day O'Connor, an opening on the Supreme Court offers President Bush the opportunity to alter the course of American jurisprudence, and the alliance between Republicans and religious conservatives has reached the moment that many of those conservatives believe is long overdue.

For a quarter-century, a politically awakened movement of conservative evangelicals and moral traditionalists of other faiths has played an increasingly important role in Republican electoral successes. In campaigns, they have knocked on doors, stuffed envelopes and dependably performed the other mundane but essential work behind winning elections. At the polling place, they have provided a crucial bloc of votes.

Bush would not be in the White House today without their support. Half of his votes in the 2004 election came from religious traditionalists, according to a survey by the politically independent Pew Research Center. And heavy support from evangelicals gave him the margin of victory in such battleground states as Ohio, Florida, Iowa and Missouri.

Yet religious conservatives so far have not had much success on the issues that matter most to them. Reagan gave them hope but little in the way of action. The first President Bush never seemed quite comfortable talking about their issues.

Abortion remains readily available, with few legal restrictions. The gay-rights debate has moved from employment discrimination to marriage equality. Pornography is more accessible than ever. And the Ten Commandments were just thrown out of courthouses in Kentucky.

It is a source of frustration to some leaders of the movement.

And they have not been quiet in criticizing even a prospective Bush nominee to the Supreme Court whom they deem insufficiently devoted to their cause. A torrent of criticism from social conservatives flowed when news reports suggested that Bush might nominate his friend Attorney General Alberto Gonzales, whose views on abortion rights are considered murky.

"We have very little to show for all these years of electing Republicans. If we don't get a decent nominee, we've got to ask ourselves what we've been doing," said Paul Weyrich, a longtime leader of social conservatives who helped found the Moral Majority and is now chairman and CEO of the Free Congress Foundation.

"For President Bush, social conservatives and the senators they helped elect, the moment of truth has arrived," said Richard Land, head of the public-policy agency for the Southern Baptist Convention, the nation's largest non-Catholic denomination.

Religious conservatives heard Bush the candidate regularly tout Supreme Court Justices Antonin Scalia and Clarence Thomas as models for a judicial nominee. They understood that to mean someone who, like Scalia and Thomas, adheres to a narrow, "strict constructionist" reading of the Constitution that does not find a basis for rights to abortion, homosexual sex or sale of pornography, and allows a greater role for religion in public life.

Anything less, or any effort to split the difference, by picking one strong conservative and one more-moderate candidate if conservative Chief Justice William Rehnquist should resign this summer, "would be a grave error, a missed opportunity and a betrayal," said Phyllis Schlafly, founder of the Eagle Forum.

Social conservatives have had mixed success with the Supreme Court nominations of the Republican presidents they supported. Reagan gave them the strongly conservative Scalia, but also O'Connor and Anthony Kennedy, both moderates. The first President Bush appointed Thomas but also solidly liberal David Souter.

The replacement of O'Connor with a justice who rules against abortion rights would not in itself be sufficient to overturn Roe v. Wade, for which there appears to be a 6-3 majority among current members of the court.

But such an appointment seems necessary if the decision is to be overturned in the near future. The ailing chief justice votes against abortion rights anyway. Besides O'Connor, the only Roe supporter on the court who seems likely to leave soon is 85-year-old Justice John Paul Stevens. The others who vote to uphold Roe are much younger.

"When you look at the arithmetic and actuarial tables, if Mrs. O'Connor is not replaced by a strong, strict-constructionist conservative, then it's hard to see how the court will be turned around in this generation," Land said.

More immediately, Bush's nominee to replace O'Connor could play a pivotal role on church-state issues. O'Connor provided the decisive vote in last month's 5-4 ruling removing the Ten Commandments from Kentucky courthouses, as well as an earlier 5-4 ruling banning prayer at public-school graduations.

The Rev. Tim LaHaye, author of the popular "Left Behind" Christian book series and one of the evangelical leaders who 25 years ago left the meeting with Carter so deeply disappointed, said the importance of the choice facing Bush is unmistakable.

"This is a very, very significant moment, and it will become more and more significant," LaHaye said.