WASHINGTON -- Average fixed rates on U.S. long-term mortgages neared their highs for the year this week amid signs of further strength in the economy.Mortgage buyer Freddie Mac said Thursday that the average rate on the 30-year loan was 4.57 percent this week. That's up from 4.51 percent last week and close to the high this year of 4.58 percent reached Aug. 22.The average on the 15-year fixed mortgage rose from 3.54 percent to 3.59 percent. That's near the year's high of 3.6 percent.Long-term mortgage rates have risen more than a full percentage point since May, when Chairman Ben Bernanke first signaled that the Federal Reserve could reduce its bond purchases later this year if the economy continued to strengthen. The bond purchases have been intended to keep long-term loan rates ultra-low.Among the indicators the Fed will weigh in deciding whether to slow its bond buying is the government's estimate that the economy grew at a 2.5 percent annualized rate from April through June -- much faster than previously estimated. Economists expect growth to stay at an annual rate of about 2.5 percent in the second half of the year.The Fed will meet Sept. 17-18, after which most analysts expect it to announce that it will scale back its bond purchases.Mortgage rates remain low by historical standards. But the recent increases in rates could slow the housing recovery's momentum. The increases have spurred some homebuyers to close deals quickly.U.S. sales of newly built homes dropped 13.4 percent in July to a seasonally-adjusted annual rate of 394,000, the lowest level in nine months.But spending on construction projects rose in July to its highest level since June 2009, the Commerce Department said Tuesday.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 stimulus to the economy.The 10-year note's rate rose to 2.89 percent Wednesday from 2.86 percent Tuesday. It jumped to 2.96 percent Thursday morning.To calculate average mortgage rates, Freddie Mac surveys lenders across the country 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 unchanged at 0.7 point. The fee for a 15-year loan also held at 0.7 point.The average rate on a one-year adjustable-rate mortgage increased to 2.71 percent from 2.64 percent. The fee rose to 0.5 point from 0.4 point.The average rate on a five-year adjustable mortgage rose to 3.28 percent from 3.24 percent. The fee was unchanged at 0.5 point.