"The idea of having a fence around the Ten Commandments to make clear the state has nothing to do with it, I think that is bending it too far," said acting Solicitor General Paul Clement, in arguing against a strict First Amendment wall between church and state.
David Friedman, an attorney for the American Civil Liberties Union who is challenging courthouse displays in Kentucky countered: "An assertion that the Ten Commandments is the source, the foundation of our legal system ... that is simply wrapping the Ten Commandments in the flag, and that's endorsement."
In their comments and questions from the bench, justices were reluctant to adopt a blanket ban on such displays. They struggled to formulate a clear constitutional rule that could determine the fate of thousands of religious symbols on public property around the country, including one in their own courtroom featuring Moses holding the sacred tablets.
Justice Antonin Scalia noted that legislative proclamations and prayer invoking God's name are permissible. "I don't see why the one is good and the other is bad," he said.
In the high court's first confrontation with the Ten Commandments issue in a quarter-century, a case from Texas also was being argued.
Erwin Chemerinsky, a lawyer representing a man who seeks its removal, told the justices the display is a "religious symbol." The prominence of the display on the capitol grounds and the fact that so many of the commandments deal with God "does promote religion," he maintained.
Monuments carrying the Ten Commandments are common in town squares, courthouses and other government-owned land around the country. Lawyers challenging these displays argue that they violate the First Amendment ban on any law "respecting an establishment of religion."
The question has sparked dozens of heated legal battles, including one in Alabama by Roy Moore. He lost his job as chief justice a year ago after defying a federal order to remove a 5,300-pound Ten Commandments monument he had installed in the state courthouse.
More than 50 groups have filed "friend-of-the-court" briefs weighing in on the issue.
Outside, nearly a hundred demonstrators gathered in front of the Supreme Court in the icy cold for rallies following a candelight vigil by supporters of the displays. Many shouted "Amen" and broke into refrains from "Amazing Grace," as in the form of a prayer meeting, as several kneeled before the court steps.
Opponents of the displays, meanwhile, waved signs reading "Keep Government and Religion Separate" and "My God Does Not Need Government Help."
"I don't think government should be in the business of morality," said David Condo, 40, of Beltsville, Md.
While the cases strictly involve Ten Commandments displays, a broad ruling could define the proper place of religion in public life — from use of religious music in a school concert to students' recitation of "under God" in the Pledge of Allegiance. A decision is expected by late June.
The Bush administration, which sided with a California school district last year to keep "God" in the Pledge, is now joining Texas and Kentucky officials to back the Ten Commandments displays.
Ten Commandments displays are supported by a majority of Americans, according to an AP-Ipsos poll. The poll taken in late February found that 76 percent support it and 23 percent oppose it.
In the Texas case, Thomas Van Orden lost his lawsuit to have a 6-foot granite monument removed from the state Capitol grounds.
The Fraternal Order of Eagles donated the exhibit to the state in 1961, and it was installed about 75 feet from the Capitol in Austin. The group gave thousands of similar monuments to American towns during the 1950s and '60s, and those have been the subject of multiple court fights.
Two Kentucky counties, meanwhile, hung framed copies of the Ten Commandments in their courthouses and added other documents, such as the Magna Carta and the Declaration of Independence, after the American Civil Liberties Union challenged the display.
While one lower court found the Texas display to be predominantly nonreligious because it was one of 17 monuments in a 22-acre park, another court struck down the Kentucky displays as lacking a "secular purpose." Kentucky's modification of the display was a "sham" for the religious intent behind it, the Cincinnati-based 6th U.S. Circuit Court of Appeals ruled.
"With clear factual distinctions between the two cases, the justices could take the easy way out and declare Texas' display valid while striking down the displays in Kentucky," CBSNews.com Legal Analyst Andrew Cohen.
"I'm hoping they don't. I'm hoping (but not expecting) that the justices come up with a that provides once and for all clear rules in this area of the law."
The last time the Supreme Court weighed in on the issue was 1980, when it struck down a Kentucky law requiring Ten Commandments displays in public classrooms. Since then, more than two dozen courts have ruled in conflicting ways on displays in various public contexts.
Justices have outlined several different tests in recent years to determine their constitutionality:
The Supreme Court frieze, for instance, depicts Moses and the tablets as well as 17 other figures including Hammurabi, Confucius, Napoleon and Chief Justice John Marshall. Because it includes secular figures in a way that doesn't endorse religion, the display would be constitutional, Justice John Paul Stevens suggested in a 1989 ruling.
The cases are Van Orden v. Perry, 03-1500, and McCreary County v. ACLU, 03-1693.