The Federal National Mortgage Association, the government-chartered company created to increase the availability of home loans, said yesterday its second-quarter earnings soared 50 percent on the strength of its financial market dealings.

Fannie Mae said its second-quarter earnings, its 10th consecutive quarter of record results, were $289.6 million ($1.10 a share), up from $193 million (75 cents) in the second quarter last year. For the first half of 1990, the company reported earnings of $566 million ($2.15), up 58 percent from $358 million ($1.39) for the same period last year.

"They've done an incredible job," said Eric I. Hemel, an analyst with First Boston Corp. in New York. He said Fannie Mae's strong results were partly because of the company's strong management and partly due to "being in the right place at the right time."

Morgan Stanley analyst Nancy G. Spady said the earnings report showed that the company's credit quality figures were strong and that its expenses were under control. "The company is still building capital, and that's keeping up with their growth," Spady said.

Fannie Mae buys mortgages from primary lenders, such as mortgage bankers and savings and loans, which in turn use the money to make more home loans. The company raises funds by selling Fannie Mae bonds and other securities to investors.

Its quarterly report showed that its capital, defined as shareholder equity plus allowances for losses, was $4 billion at the end of the second quarter, up more than 33 percent from $3 billion a year ago.

Analysts said the earnings were slightly higher than expected, and they believe the company will keep growing, though not at the same pace. Fannie Mae stock closed yesterday at $42.62 1/2, up 87 1/2 cents.

Fannie Mae Chairman David O. Maxwell attributed the earnings increase to continued strength in the company's investment portfolio and in one of its complex specialties, the mortgage-backed securities business. The company also said that acquisition of foreclosed properties fell to the lowest level since 1984, a positive development since Fannie Mae loses money when homeowners default.