LOS ANGELES — Banks are increasingly placing homes with unpaid mortgages on a countdown that could deliver a swell of new foreclosed properties onto the market by early next year, potentially weighing further on home values.

June provided the latest evidence of this trend, as the number of U.S. homes entering the foreclosure process for the first time increased on an annual basis for the second month in a row, foreclosure listing firm RealtyTrac Inc. said Thursday.

California in particular saw a big spike in foreclosure starts, or homes placed on the foreclosure path for the first time. They increased 18 percent versus June last year, the firm said.