For the Rev. Jerry Falwell, the battle to replace retiring Supreme Court Justice Sandra Day O'Connor isn't quite Armageddon, but almost.

"This is do or die," Falwell said Friday.

For religious conservatives who have spent more than 25 frustrating years toiling in the political vineyards only to see their positions on many key issues — abortion, gay rights, church-state disputes — rejected by the high court, O'Connor's retirement is the moment they have been waiting for.

The contentious fight over her replacement will be perhaps the most important test of their organization and political clout. If they don't win on this one, Falwell said, there's little hope for much else.

The court opening is especially crucial because, as conservative religious leaders have learned, presidents may come and go, but Supreme Court justices tend to remain for a generation or more.

At the same time, a re-energized progressive faith community that emerged in last year's elections faces an uphill challenge in trying to steer the court down a more centrist path, a fight in which activists say the stakes are equally high.

"Conservative Christians did play a major role in helping elect George Bush twice, and they haven't gotten all that much in return," said Alan Wolfe, director of the Boisi Center for Religion and American Public Life at Boston College.

"This is the one that is important to them."

The recent Senate fight over lower-level judicial nominees only reinforced how much conservatives want to see an end to "activist judges" whom they accuse of making law, not interpreting it. In many ways, the courts — and especially the Supreme Court — have become ground zero for every issue on the conservatives' agenda.

Leaders of the Christian ...