HONGKONG's 4As advertising association published its billings figures earlier this month but held back on announcing the separate China totals because some members could not submit audited income figures. Mr Peter Stening, chairman of the 4As, said that agencies which had opened offices in China in 1992 would suffer significant costs by implementing an audit within their first year of operation. ''We decided to let it pass this year because it's unrealistic to expect them to incur those kind of auditing costs,'' he said. The first audited China Income report from the 4As will be reported next year, for 1993 results. But some agencies have already revealed their capitalised billings figures for 1992. Dividing the totals by seven gives a rough idea of their income from China. Leo Burnett's China billings, much of it netted from Marlboro, reached $135 million last year. Dentsu, Young and Rubicam reported total billings of $116 million.