WASHINGTON --Americans bought fewer previously occupied homes in September after hitting a two-year high in August.The National Association of Realtors says sales dipped 1.7 percent to a seasonally adjusted annual rate of 4.75 million. That's down from a rate of 4.83 million in August, which was the highest in more than two years. Sales are still up 11 percent from a year earlier, further evidence that the housing market is slowly recovering. But sales remain below the more than 5.5 million that economists consider consistent with a healthy market. The inventory of homes for sale fell in September to 2.32 million. It would take 5.9 months to exhaust the supply at the current sales pace, the lowest sales-to-inventory ratio since March 2006.