WASHINGTON » Average U.S. rates on fixed mortgages fell for the third straight week to their lowest point in three months, as a decline in consumer confidence and the onset of the government shutdown forced rates down.

Mortgage buyer Freddie Mac said today that the average rate on the 30-year loan dropped to 4.22 percent from 4.32 percent last week. The average on the 15-year fixed loan declined to 3.29 percent from 3.37 percent.

Both are the lowest averages since early July.

Rates began to fall last month after the Federal Reserve held off slowing its $85-billion-a-month in bond buys, which have kept rates low. They fell further this week as the shutdown prompted investors to sell stocks and buy Treasury bonds. Mortgage rates tend to follow the yield on the 10-year Treasury note.

The 10-year note traded at 2.63 percent this morning, down from 2.71 percent on Sept. 23.

The Federal Housing Administration, which guarantees about 30 percent of U.S. home mortgages, says that if the partial shutdown continues for an extended period and the agency’s funding runs out, it wouldn’t be able to continue approving loans.

In that case, "We do expect that potential homeowners will be impacted, as well as home sellers and the entire housing market," the FHA said in a contingency plan.

Buyers wouldn’t disappear. But some would linger in limbo until the government reopened and a backlog of applications cleared.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country on Monday through Wednesday each week. The average doesn’t include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1 percent of the loan amount.

The average fee for a 30-year mortgage was steady at 0.7 point. The fee for a 15-year loan also was unchanged at 0.7 point.

The average rate on a one-year adjustable-rate mortgage was unchanged at 2.63 percent and the fee held at 0.4 point.

The average rate on a five-year adjustable mortgage dipped to 3.03 percent from 3.07 percent. The fee rose to 0.6 point from 0.5 point