THE Director of Audit will investigate the Hong Kong Stadium controversy if he receives an official request from legislators. United Democrat Cheung Man-kwong has demanded an inquiry into the cost of the sports ground which he described as a ''white elephant''. The stadium, which opened last month, has been criticised as unsuitable for pop concerts because of the noise level, and unsuitable for local sports events because of the high rents. Although no public money was involved director Brian Jenney stressed the stadium was government property. The $850 million redevelopment cost was borne by the Jockey Club and the $175 million fitting out cost was drawn from the Urban Council. But because legislators had suggested a special select committee conduct open hearings, he had not made a decision. Both the Liberal Party and independent legislator Emily Lau Wai-hing have called for the setting up of a select committee to examine the stadium's noise problem. Their call came after hearing that advice from the Environmental Protection Department about the unsuitability of the stadium to stage rock concerts was ignored. by the Jockey Club, Urban Services Department and the stadium manager.