President Barack Obama urged Americans on Saturday to recall the spirit that united the country after the Sept. 11 attacks and take part in a national day of service to mark the anniversary next month."As we mark this solemn anniversary, let's summon that spirit once more. And let's show that the sense of common purpose that we need in America doesn't have to be a fleeting moment; it can be a lasting virtue," Obama said in his weekly radio address."But even if you can't be in New York, Pennsylvania or Virginia, every American can be part of this anniversary. Once again, 9/11 will be a National Day of Service and Remembrance," Obama said.Obama and his wife Michelle will mark the 10th anniversary of the attacks by visiting Ground Zero in New York, the Pentagon, and the site in Shanksville, Pennsylvania, where the fourth hijacked airline crashed after its passengers.