WASHINGTON—Contracts to buy U.S. previously owned homes rebounded to a seven-month high in August, but higher prices amid tight supply are slowing the housing market momentum. The National Association of Realtors (NAR) said on Wednesday its Pending Home Sales Index, based on signed contracts, jumped 8.1 percent last month to 119.5. That was the highest reading since January and followed two straight monthly declines. Economists polled by Reuters had forecast contracts, which become sales after a month or two, increasing 1.4 percent. Compared with a year ago, pending home sales fell 8.3 percent in August. The housing market boomed early in the COVID-19 pandemic amid an exodus from cities as people worked from home and took classes online. But the pandemic tailwind is fading as vaccines allow workers to return to offices. Expensive homes are also sidelining some first-time buyers from the market. The NAR reported last week that the …