ROBERT Fleming & Co. yesterday announced plans to issue 60 million call warrants on Hong Kong and China Gas. The British merchant bank said the call warrants would be issued at $4.625 each, entitling the holder to buy one existing share of Hong Kong and China Gas. The call warrants will have a strike price of $21 and be exercisable from December 9, 1993 to November 16, 1995. Hong Kong and China Gas closed yesterday at $20.90. The call warrants will be placed by Robert Fleming and Jardine Fleming International with professional investors and securities dealers through a private placement. Last month, Robert Fleming issued 80 million covered warrants on CITIC Pacific shares. This came on the heels of a two-year, 250 million covered-warrant issue on Hopewell Holdings in September.