WASHINGTON — A fixture since President Harry S. Truman signed a bill proclaiming a National Day of Prayer 58 years ago, 2010 could be the last time the event is observed if the White House fails in an appeal against a court ruling that it violates the ban on government-backed religion.

Wisconsin-based U.S. District Court Judge Barbara Crabb ruled April 15 in favor of the Freedom From Religion Foundation in a suit brought against President Barack Obama. She ruled that the federal law that designates a National Day of Prayer and requires an annual presidential proclamation of the National Day of Prayer violates the establishment clause of the Constitution's First Amendment.

Despite that ruling, several observances took place around the capital Thursday, including at the Pentagon, the Cannon House Office Building and on the steps of the U.S. Capitol. In her decision, Crabb said until the defendants in the case exhaust their right to appeal the decision, observance ceremonies could still go ahead.

The Freedom From Religion Foundation, a national membership association of free thinkers based in Madison, Wis., held a rally protesting the day of prayer on the steps of the Wisconsin state Capitol.

Charles Haynes, a senior First Amendment scholar specializing in religious liberty at the Washington-based Freedom Forum, said he expects the president to succeed with his appeal. But he said Crabb was merely being consistent with past rulings and essentially saying "what everybody knows about the inherent (constitutional) contradiction of the National Day of Prayer."

"The courts are not immune to public dissatisfaction," he said, adding the Court of Appeal could possibly cite a 1983 Supreme Court decision that upheld the right to legislative prayer, on grounds "the offering of prayer is a tolerable acknowledgment of beliefs widely held among the people of this country."

"It is possible the courts would argue that the Day of Prayer goes all the way back to our Founding Fathers and that they are not going to disturb it," he said. "Prayer, in this case, is merely 'ceremonial deism."'

In a separate development, evangelist Franklin Graham prayed on a sidewalk outside the Pentagon Thursday after the Army decided two weeks ago to rescind an invitation to their National Day of Prayer service following an objection by the Military Religious Freedom Foundation that Graham had previously insulted people of other religions, particularly Islam.

Graham is the honorary chairman of the private National Day of Prayer Task Force that leads national events where all the prayers are strictly Christian. The Army said its leadership decided Graham's past comments were "inappropriate as a speaker for an open religious service."

Haynes said the National Day of Prayer was an attempt to unify people of different faiths, but fights have become more common in the last few years in part due to the prominence the George W. Bush administration accorded to private evangelical Christian groups such as National Day of Prayer Task Force, promulgating the perception that the government was endorsing a sectarian religious approach.

"Presidents may be required to make the proclamation," he said. "But they can choose to make it a big deal. President Obama's approach is more consistent with the treatment of prayer as a form of 'ceremonial deism."'