Ambassador Herbert S. Okun, deputy U.S. representative to the United Nations, denied published charges that he and other U.S. diplomats are living it up at government expense on Manhattan's expensive upper East Side. The deputy to Ambassador Vernon A. Walters said Foreign Service officers at U.S. embassies get free housing and are assessed 5% of their annual salary as their only contribution. "Here in New York, we pay 10% of salary as a contribution toward housing," Okun said. Okun, who is responsible for administration at the 200-member U.S. mission to the United Nations, rejected other assertions of excessive spending in a confidential State Department report. He described the report as a routine one made by the State Department's inspector general and leaked by what he called a "disgruntled former foreign service officer."