Prime Minister Sharon departed last night for his sixth visit to Washington since taking office 15 months ago. He will try to strengthen the position of those who say that Arafat must be totally marginalized, and will present his own diplomatic initiative. Bush, who met with Egyptian President Hosni Mubarak yesterday, said he had no timetable regarding the establishment of a Palestinian state, and again expressed his disappointment in PA leader Yasser Arafat.