RALEIGH, N.C. — Nine justices, no Protestants.

If the Senate confirms Solicitor General Elena Kagan as the next Supreme Court justice, the result will be an anomaly in a country that has been dominated by Protestants since the Pilgrims.

Kagan, nominated Monday by President Barack Obama, would be the third Jewish justice, and would join six Roman Catholics on the court, meaning none of the justices would be rooted in the Protestant Reformation traditions that shaped the country from its earliest stages.

That could show Americans are far more accepting of religious diversity than they were a generation ago, when John F. Kennedy's presidential campaign was dogged by suspicions about his Catholic faith. But it also might be a sign of the approaching time when Protestants lose their majority status.

"I don't think this means Protestant America is over, but I do think it means the old way of thinking about Protestant America is over," said Stephen Prothero, a professor of religion at Boston University and author of "God Is Not One."

The possibility of a Supreme Court without Protestants is just a dramatic illustration of what observers of religion have known for years, Prothero said: that in a country where President John Adams could once say Roman Catholics were "as rare as a comet or an earthquake," Protestants have seen their share of the population dramatically shrink.

"The population is probably just over 50 percent Protestant," said Mark Chaves, a professor at Duke University who directs the National Congregations Study. "It's heading down, though, and any minute now it will probably drop below 50 percent."

Membership in "mainline" Protestant churches has been falling for decades, sapping the ranks of Episcopalians, Congregationalists, Presbyterians, Methodists, Lutherans and others who for years defined American mainstream religion.

Even that declining share of the population, though, doesn't make a ready explanation for the prospect of a court without any Protestants

"You'd predict Protestants would be either four or five based on their proportion of the population, but instead it looks like they'll be zero," Smith said. If confirmed, Kagan would replace Justice John Paul Stevens, a Protestant.

That's troubling if the court is supposed to reflect a diversity of opinion, says Baylor Law School Professor Mark Osler.

"There's an important part of our population that's not represented here," Osler said. "We have to recognize that faith plays into the development of conscience in the same manner that race and gender do, and perhaps more so."

There's no single factor that accounts for the disproportionate share of Catholics and Jews on the court, given that the eight non-Protestant justices were appointed over a period of 23 years by five different presidents.

Ideological affinity, along with categories like race and gender, seem to have played a greater role than religious affiliation.

"I think it's an accident of history," Osler said. "Presidents have been looking for other types of diversity."