A Metro-North train traveling from Bridgeport to Waterbury hit a dump truck at a Milford crossing yesterday afternoon, and six people were taken to hospitals with minor injuries. It was unclear how long it might take to get the train running again, Dan Brucker, a Metro-North spokesman, said. The train, carrying 51 people, hit the truck just before 2 p.m. at the Gulf Street crossing, Mr. Brucker said.