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As observers celebrate the National Day of Prayer Thursday, a recent court ruling and Army decision to revoke an invitation to evangelist Franklin Graham has shrouded in controversy a day meant for reflection and prayer.

Graham, honorary chairman of the 2010 National Day of Prayer Task Force, prayed on sidewalk outside the Pentagon anyway on Thursday, despite the decision to rescind his invitation to participate amid complaints about his describing Islam as an evil religion.

After praying, Graham told reporters he came because he cares about the troops fighting in Afghanistan.

"I have a son in Afghanistan and I came today to pray for our men and women that serve this nation," he said. "They risk their lives every day to protect our freedom. So my prayer was that God would watch over them."

Religious leaders and government officials are holding events Thursday to mark the 59th observance of the day, including capping off a marathon Bible reading in Washington, D.C., that began Wednesday.

The event, created in 1952 and signed into law by President Harry Truman, was amended in 1988 by President Ronald Reagan to state that the day would be observed on the first Thursday in May. Organizers cite the day of prayer's origins to 1775 when the Continental Congress encouraged the colonies to pray for wisdom in forming a nation.

President Obama issued a proclamation last Friday as his Justice Department appeals a federal judge's ruling last month that the day of prayer is unconstitutional.

"Prayer has been a sustaining way for many Americans of diverse faiths to express their most cherished beliefs, and thus we have long deemed it fitting and proper to publicly recognize the importance of prayer on this day across the Nation," Obama said in the proclamation.

But critics note that Obama, unlike his predecessors, has not held a traditional White House prayer service since he took office.

"Every time I hear the president casually end a speech with 'God Bless America,' I wonder if he realizes that phrase is a prayer -- not another edict from Washington," said Andrea Lafferty, executive director of the Traditional Values Coalition.

"I can't remember a time when America was more in need of God's blessing, but the president doesn't see it," she said.

The lawsuit challenging the day of prayer was brought by the Freedom From Religious Foundation, a Madison, Wis.-based group of atheists and agnostics. Protests were expected there and in Washington.

The lawsuit was originally filed against President George W. Bush's administration near the end of his second term. The foundation argued the day violates the separation of church and state.

Some religious groups agree with the foundation's claim. K. Hollyn Hollman, general counsel of the Baptist Joint Committee for Religious Liberty, said every day should be a day of prayer, but the official designation and the president's proclamation are "misguided and unnecessary."

"A day of prayer is more appropriately called for by our religious leaders - not civil magistrates, Congress or even the president," Hollman said in a statement issued Wednesday. "There is nothing wrong with the American people getting together to pray on a designated day, even public officials. ... The problem with the National Day of Prayer is that it is an official act of the government urging citizens to engage in a religious exercise."

But Sen. John Cornyn, R-Texas, disagreed, saying prayer has "enriched American public life and inspired us to become a more perfect union" and "has blessed every day of business in the United States Senate."

"This year the National Day of Prayer faces a new challenge in the courts," he said in a written statement. "The case reminds us that our First Amendment freedoms will not survive if we fail to defend them."

Expecting her ruling to be challenged, U.S. District Judge Barbara Crabb said in her decision last month that the National Day of Prayer can continue until the legal process is exhausted.

Graham said he is grateful that the Justice Department is appealing the ruling. He added that he has twice been to the Pentagon since Sept. 11, 2001, and preaches to military chaplains.

On Thursday, he arrived in the Pentagon parking with his party of a half dozen people forming a circle on the sidewalk and praying.

They stood there for about five minutes, heads bowed, as people arriving for work passed by.

Then the group walked to the Pentagon's Sept. 11, 2001 memorial roughly a couple of hundred feet (meters) away, where media had gathered because it is one of the few places were cameras are allowed on the Pentagon property. There, Graham held a news conference that lasted nearly twice as long as the prayer.

He said he doesn't believe "all religions are equal" and that there is only "one way to God" -- and that is through Jesus.

Asked if he still believes Islam is evil, he said: "I believe the way they treat women is evil, yes I do." And, can he understand how some of his comments would be offensive to Muslims? "Oh, I'm sure," he said. "But I find what they teach and what they preach and what's on the Internet -- I find that to be offensive, too."

While Graham spoke outside, some 80 people attended a service inside the Pentagon that included Roman Catholic, Jewish, Muslim and Protestant chaplains.

Pentagon spokesman Geoff Morrell described Graham's appearance as "pretty uneventful."

"He came, he prayed, he left," he said. "I guess he spent a little more time talking with you all than he did praying. But overall, I think it went well."

The Army's decision to withdraw its invitation is still catching flak. Thirty-six members of the House sent a letter to Defense Secretary Robert Gates urging him to reconsider the military's decision.

"To rescind Franklin Graham's invitation for these overtly political reasons is a disgrace that is obviously being done to placate a few outspoken critics, and an affront to those ideals that are the essence of America and that are reflected throughout America's history," said Rep. Trent Franks, R-Ariz.

"Not everyone will agree with all that Rev. Graham has to say," Rep. Mike Pence, chairman of the House Republican Conference, said. "But we can agree that our Constitution protects his right to say what he believes."

Fox News' Shannon Bream, Justin Fishel and The Associated Press contributed to this report.