WHEN fishermen on the rocky shores of Ko Lau Wan invoke the sea goddess Tin Hau these days, they are more likely to ask her to safeguard the speedboats of smugglers than their own weatherworn junks.This isolated settlement on Hong Kong's northern coast was known until recently as a major smuggling den. The straw-hatted villagers gave up fishing and netted thousands of dollars ferrying TV sets and other goods onto speedboats bound for China's insatiable market. At any one time, an estimated 100,000 TV sets crowded the homes of Ko Lau Wan's 100 natives. A Hong Kong crime syndicate had set up legally registered electronics companies in the village to protect the huge stock of TV sets. Last May, a police blockade nearly put Ko Lau Wan out of business, forcing fishermen to return to their nets. Hong Kong police are still stationed at the Ko Lau Wan dock and often search village vessels. As a result, police say, many fishermen have resorted to "the golden hook," a less conspicuous form of smuggling using their motorized sampans. In offshore deals, they trade cargos of TVs and other smuggled goods for the catches of mainland fishermen.