The New York State Police are deploying more assets on the South Fork, leading to more arrests on alcohol-related charges. “We’re focusing on the midnight tours,” Sgt. James Marrone said Tuesday. “We’re sending out at least one vehicle when we have a car available.” Besides making arrests on driving while intoxicated charges, state police have also launched an operation to catch those who sell alcohol to under-age drinkers. On Friday, state troopers targeted 10 South Fork businesses — four in Sag Harbor and six in Montauk — resulting in four arrests, all charged with unlawful dealing with a child, a misdemeanor, and prohibited sale of an alcoholic beverage, a violation, state police said. All four were released with appearance tickets. Police wrote up Marc S. Cohen, 63, of Sag Harbor, the owner of Water Street Wines and Liquors in that village, Segundo F. Tacuri, 39, of East Hampton, the owner of Nelly’s Deli in Montauk, Caralyn C. Brown, 31, of Montauk, a clerk at the Marshall and Sons gas and food mart in that hamlet, and Susan C. Maynard, 60, of Montauk, a clerk at Montauk Liquors and Wines. Under-age agents were sent into each establishment, along with a trooper in plain clothes. The under-age agents were given identification that reflected their actual age and were instructed to tell the truth if they were asked how old they were, state police said.