WASHINGTON » Average U.S. rates on fixed mortgages held steady this week, hovering near two-year highs. But rates could change quickly next week when the Federal Reserve addresses its bond purchase program.

Mortgage buyer Freddie Mac said today that the average rate on the 30-year loan was unchanged from last week at 4.57 percent, just below the two-year high of 4.58 percent reached Aug. 22.

The average on the 15-year fixed mortgage held at 3.59 percent. The two-year high of 3.60 percent was hit on Aug. 22.

Long-term mortgage rates have risen more than a full percentage point since May, when Chairman Ben Bernanke first signaled that the Fed could reduce its bond purchases this year. The purchases have been intended to keep long-term loan rates extremely low.

Most analysts expect the Fed to decide at its meeting next week to scale back its bond purchases.

Even with the recent gain, mortgage rates remain low by historical standards. But higher rates have spurred some homebuyers to close deals quickly and could slow the market’s momentum if they continue to rise.

Mortgage rates have been rising because they tend to track the yield on the 10-year Treasury note. The yield has climbed 1.3 percentage points in the past four months as bond traders have anticipated that the Fed will slow its bond buying.

The 10-year note’s rate was 2.92 percent on Wednesday, down from 2.97 percent Tuesday but up from 2.89 percent a week earlier.

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 rose to 0.8 point from 0.7 point. The fee for a 15-year loan was steady at 0.7 point.

The average rate on a one-year adjustable-rate mortgage fell to 2.67 percent from 2.71 percent. The fee declined to 0.4 point from 0.5 point.

The average rate on a five-year adjustable mortgage dipped to 3.22 percent from 3.28 percent. The fee was unchanged at 0.5 point.