A NEW series of options offering investors exposure to Hong Kong stocks during North American trading hours was launched last night on the American Stock Exchange in New York. The option series is based on the Hong Kong Option Index. A spokesman for the exchange said last night: ''The series is intended to increase access to what many US investors call the gateway to China.'' The regular and reduced value long-term options began trading last night at 8 am New York time. James Lilley, a former ambassador to China and Paine Webber senior vice-president, and Christopher Berry, manager of structures products and Hong Kong expert, officiated at the launch of the series. The Amex 30 index consists of the 30 most highly capitalised Hong Kong stocks. The Amex Hong Kong index of regular term options (HKO) and Long-term Equity AnticiPation Securities (LEAPS), or reduced value long-term options, are based on the Amex 30 index. ''The HKO was created by Amex to measure the performance of the Hong Kong market as a whole,'' said a spokesman for Amex. The Amex index represents two-thirds of the market's capitalisation, while LEAPS is one tenth the value of the HKO index. Amex's executive vice-president of derivative securities said: ''Now, at last, there will be a wide array of new opportunities for investors to seek either profit or protection from price movements in the dynamic Hong Kong stock market.'' Hong Kong index options can benefit investors who have holdings of Hong Kong stocks or are interested in participating in the fluctuations in the market as a whole, without wanting to invest in individual underlying stocks. The options will be cashed in US dollars. At the start of trading, the index stood at 167.45. Options opened with strike prices at 165, 170, 175, 180, 185, 190 and 195. LEAPS, expiring in January 1995 and January 1996, had strike prices of 15 and 20.