CAIRO, April 5 (Reuters) - Egypt's top Islamic cleric gave his blessing on Saturday to volunteers wishing to help Iraqis in the war against U.S. and British forces, but blamed Iraqi President Saddam Hussein for the conflict. Mohammed Sayed Tantawi, the state-appointed grand sheikh of al-Azhar mosque and university in Cairo, said the war on Iraq was an attack on all Arab countries, but added that Saddam could have avoided it by going into exile. "Whoever wants to go to Iraq to support the Iraqi people, the door is open, and I say the door for Jihad (holy struggle) is...