A former North Hempstead budget official pleaded guilty yesterday to having sex with a 16-year-oldgirl who had told him by e-mail that she was 18, prosecutors said. Owen Sinclair, 46, of Oceansidepleaded guilty to endangering the welfare of a child. He had faced more serious statutory rapecharges for having sex with the girl twice at a Lynbrook motel, said Eric Phillips, a spokesman forNassau District Attorney Kathleen Rice. Sinclair is expected to receive probation when he issentenced May 27, Phillips said. It is illegal for an adult to have sex with a child, even whenunaware that the child is underage. Despite the fact that the investigation confirmed that thevictim had consistently misrepresented her age to the defendant and others, the DA felt it wascritical to hold the defendant accountable for his actions, Phillips said. Sinclair's lawyer,Brian Griffin of Garden City, said the fact that his client's charges were reduced shows that hedidn't know he was doing anything wrong. He believed he was having an adult consensualrelationship, Griffin said. Ultimately the substantial reduction in the charges proves that theauthorities agreed that Mr. Sinclair had been deceived. Sinclair was fired from his $100,000 ayear job as North Hempstead's deputy director of finance shortly after his arrest. He had held thejob for less than a month, a town spokesman said. The girl, of Brooklyn, whose name is not beingreleased because she is a sex-crime victim, was charged with criminal impersonation afterrepeatedly lying to police about her age, and her case is pending, Phillips said.