Two men riding all-terrain vehicles were seriously injured on Sunday when they crashed into each other in the woods behind the Montauk recycling center, East Hampton Town police said.The victims, whose names were not immediately released pending notification of their families, were riding with another man, who was on a third A.T.V., when the accident occurred at about 3:25 p.m., according to Lt. A.J. McGuire of the town police.The other A.T.V. driver was not involved in the crash. He is the brother of one of the victims, Lieutenant McGuire said.The Montauk Fire Department called for two helicopters to take the patients to Stony Brook University Hospital, the closest trauma center. Both helicopters arrived to meet the ambulances, but one of the men was not in a stable enough condition to be flown, Lieutenant McGuire said. A Montauk ambulance drove him to Southampton Hospital. Once he was stabilized, he was taken to Stony Brook by helicopter.Lieutenant McGuire said both victims were from Montauk. One is in his 20s, and the other is in his 30s. Both were wearing helmets.Detectives are investigating the accident just as they would any motor vehicle crash, Lieutenant McGuire said.