Forty-five blue-helmeted U.N. troops arrived in the Iraqi capital of Baghdad overnight and early Tuesday to begin policing the Persian Gulf war cease-fire due to begin Saturday, Western diplomats said. The troops from Canada, Poland and Senegal were the first of a total of 175 U.N. truce observers scheduled to arrive in Iraq by Wednesday, three days before the formal cease-fire with Iran takes affect, the gulf-based diplomats said. Additionally, 485 troops from Canada's 88th Signals Squadron were to arrive in the Iraqi capital to help set up the communications network the truce observers need. There was no immediate word from Tehran about the arrival of similar contingents on the Iranian side of the border.