WASHINGTON - The resurgence of consumer demand for fixed-rate loans once again fueled strong earnings at Fannie Mae and Freddie Mac in the third quarter. Earnings at Fannie Mae jumped 10% to $596.8 million. At Freddie Mac, earnings rose 12% to $278 million. Both agencies also reported increases over second-quarter levels, reflecting the continued shift of consumers from adjustable-rate mortgages to fixed-rate loans this year. At Fannie Mae, earnings rose about 4% from the second quarter. At Freddie Mac, earnings climbed about 5%. Fannie Mae and Freddie Mac took advantage of the ample supply of fixed- rate loans and the slightly wider net interest margin to build their loan portfolios. The increased supply of fixed-rate loans meant that the agencies could purchase the loans at better prices.