For the first time, interest rates on the most common home loans in the United States have fallen below 4 percent.

A large government-supported mortgage financing company, Freddie Mac, said Thursday that the average rate on traditional 30-year loans to buy a house has fallen to 3.94 percent. That is the lowest rate the company has recorded in the 40 years it has been keeping records of borrowing rates.

The dip below the 4 percent level would seem to indicate that the latest effort by the country’s central bank, the Federal Reserve, to cut long-term borrowing rates is taking hold. The central bank recently started selling shorter-term securities and buying longer-range notes in a move to boost the country’s beleaguered housing market.

Whether lowered interest rates will translate into more home sales is an open question.

The housing industry is one of the weakest sectors in the American economy, with many would-be home buyers worried about their personal finances and fearful of taking on a long-term loan commitment to buy a house. Lenders have already taken ownership of millions of American homes, forcing homeowners out of their houses when they were unable to repay their loans after losing their jobs.

Freddie Mac said that rates on shorter-term loans have fallen even lower than for 30-year notes, down to 3.26 percent for a loan that takes 15 years to pay off.