WASHINGTON — U.S. sales of existing homes fell in January from a year earlier by the most in more than three years.

Would-be buyers were stymied by rising prices and a shortage of homes for sale.

The National Association of Realtors said Wednesday that sales dropped 3.2 percent from December to January, the second straight monthly decline, to a seasonally adjusted annual rate of 5.38 million. That was the slowest sales pace since September.

Compared with 12 months earlier, sales dropped 4.8 percent — the steepest year-over-year decline since August 2014.

A lack of available homes is holding back sales, even as Realtors report that more people are visiting open houses and demand is strong. The total supply of homes for sale dipped to 1.52 million, the fewest for any January since records began in 1999.

The low inventory levels are a legacy of a decade of boom and bust in U.S. housing. Many investors bought homes at low prices during the housing bust and are now renting them out rather than selling.

And the Realtors’ group said many homeowners are reluctant to sell at a time of rising mortgage rates because they would have to pay a higher rate on a new house, a phenomenon known as “rate lock.”

The average 30-year fixed mortgage rate reached 4.38 percent last week, the highest in nearly four years. While that is still a historically low rate, for many homeowners it is much higher than their current mortgage rate.

January’s sales stem from contracts that were signed in November or December, so they don’t reflect the sharp jump in mortgage rates since the beginning of the year. The average 30-year fixed was just below 4 percent in early January.