NEW YORK — U.S. borrowers can get the cheapest mortgages this year, thanks to worries over European debt, and that could keep homebuyers active even after the expiration of a tax credit designed to increase sales.

Mortgage rates fell to their lowest level of the year this week as yields on U.S. government securities declined, Freddie Mac said Thursday. Fixed rates for mortgages tend to follow the yield of 10-year Treasury notes.

Treasury yields sank after Germany’s move this week to curtail certain kinds of short-selling spooked investors, who shifted money from risky European debt to safer U.S. securities.

A side effect of the lower Treasury rates was lower mortgage rates. The average fixed rate on a 30-year mortgage dipped to 4.84 percent from 4.93 percent a week earlier, Freddie Mac said. It was the lowest level since mid-December, when rates averaged 4.81 percent.

“The timing is fortuitous,” said Greg McBride, a senior financial analyst at Bankrate.com, “because home shoppers who rushed to sign their purchase contracts in late April to capture the tax credit are locking in their mortgage rates now.”

New buyers were offered a credit worth up to $8,000, while current owners who bought and moved into another home could get one for up to $6,500. To receive them, buyers had to have a signed offer by April 30 and must close by the end of June.

Economists expected home sales to flag after the credit expired, but lower rates could help offset the falloff.

Among other types of mortgages in Freddie Mac’s survey, the average rate on a 15-year fixed-rate mortgage was 4.24 percent this week, down from 4.3 percent. Rates on five-year, adjustable-rate mortgages averaged 3.91 percent, down from 3.95 percent a week earlier. Rates on one-year, adjustable-rate mortgages fell to 4 percent.