Dozens of Iraqi police were missing Friday and nine were dead after insurgents ambushed their convoy as they left a US base where they had picked up new vehicles, Iraqi and US officials said. Brig. Gen. Abbas Maadal complained that the Americans refused to allow the police to spend Thursday night at the base, just north of the capital. But US spokesman Lt. Col. Barry Johnson said no such request had been made and that the Iraqis had not asked for American troops to guard the convoy. The attack, the deadliest against police here in months, began about 7:30 p.m. Thursday as a convoy of 109 police was traveling through a sparsely populated area near the Taji base heading back to Najaf, 160 kilometers to the south, Maadal said.