TIKRIT, Iraq, Sept 19 (Reuters) - U.S. forces captured 40 suspected Iraqi guerrillas in a night-long battle near Saddam Hussein's hometown of Tikrit after three U.S. soldiers were killed in an ambush, a U.S. commander said on Friday. Backed by attack helicopters, U.S. troops battled guerrillas until first light after the 4th Infantry Division soldiers were ambushed and killed in part of a series of coordinated attacks east and west of the Tigris river late on Thursday. Colonel James Hickey said U.S. forces encircled an area of farmland on the east side of the river near Tikrit and captured...