Grieving family members plan to read their siblings' names out loud at Ground Zero in Manhattan Sunday to mark the fourth anniversary of the 9/11 terrorist attack that killed 2,749 people. Some 320 pairs of siblings intend to read the roll call of the victims who died at the World Trade Center. Parents and grandparents read the victims' names last year, while children's voices were heard at Ground Zero in 2003. The city has asked houses of worship to toll their bells throughout the city shortly after a moment of silence at 8:46 a.m., the time at which a hijacked jetliner crashed into the north tower. Three other moments of silence are planned: at 9:03 a.m., marking the moment a second plane struck the south tower, and at 9:59 a.m. and 10:29 a.m., the precise times when each tower collapsed. Gov. George E. Pataki, Mayor Michael Bloomberg, former mayor Rudolph Giuliani, and Secretary of State Condoleezza Rice will offer commemorative readings at the ceremony. Other memorials planned for Sunday include a Port Authority of New York and New Jersey service for the 84 employees it lost on 9/11. Firefighters plan to roll out their trucks and other equipment in front of their firehouses to observe the moment of silence. The Fire Department lost 343 firefighters in the attack. As in past years, some victims' relatives will be allowed to lay flowers at the towers' footprints. At night, two blue light beams inspired by the twin towers will be projected upward. The "Tribute in Light" will fade away at dawn on Monday.