Las Vegas expects a record tourist turnout for the Fourth of July weekend and hopes that it will kick off a reversal in the lagging visitor count for the first four months of the year. Some 226,000 visitors are expected to begin arriving today for a three-day weekend, which would surpass last year's 218,000, because the gambling mecca has more hotel rooms than ever before, according to the Las Vegas Convention and Visitors Authority. The city's room inventory--106,000--is up 2,000 from a year ago. The visitors authority expects Fourth of July tourists to generate $109.6 million in non-gaming revenue. Hotels are expected to run at about 93% occupancy for the weekend, up slightly over a year ago, said Rob Powers, spokesman for the visitors authority. "We're looking at a strong Fourth of July weekend to kick off a strong, healthy second half of 1998," he said.