A record-setting 650,000 revelers lined the sunny streets of Dublin for St. Patrick's Day, as Ireland's leaders urged the nation to honor its "most famous immigrant" - and avoid drinking too much alcohol. Dubliners and tourists packed themselves up to 20-deep on Dublin's sidewalks for Monday's parade - the centerpiece of Ireland's five-day St. Patrick's Festival. Many brought ladders or balanced precariously on security fences, garbage bins and statues to see the spectacle, which was led by a mammoth float of St. Patrick on a Harley-Davidson motorcycle. Police launched a crackdown on rowdiness and drunken driving, which typically follow the day's parading in Dublin and a half-dozen smaller Irish cities. Police said four teenagers were arrested during the parade and likely would face charges of disorderly behavior and assaulting officers. Irish Prime Minister Bertie Ahern, who was in Washington to meet U. President George W. Bush and present him with a ceremonial bowl of shamrocks, called on people back home to drink in moderation "and not to get behind the wheel after doing it."