Geico Corp. yesterday reported flat earnings for the third quarter. The Washington-based insurance company had income before investment transactions of $16.4 million compared with $16.3 million a year ago. Earnings per share were 82 cents, down from 98 cents, partly because there were more shares outstanding: 19.88 million compared with 16.098 million.

Gains from investment transactions were $1.7 million, making net income $18.1 million (90 cents), the company said. During the quarter last year, investment losses of $195,977, and an extraordinary credit from a tax loss carryforward of $5.4 million made final net income $21.5 million ($1.30). Fully diluted earnings per share, assuming that preferred shares outstanding are converted to common stock, were 76 cents compared with 64 cents a year ago.

Nine-month income before investment transactions was $44.3 million ($2.11) compared with $46.0 million ($2.62). An investment gain of $1.6 million made the final net $45.9 million ($2.19). Last year the investment gain of $1.6 million and an extraordinary gain from a tax loss carryforward of $14.2 million made final net income $61.8 million ($3.58).

The company said changes in the weighted average shares outstanding reflect the exchange of shares for debentures, repurchases of shares, the exercise of stock options and on a primary basis only a conversion of preferred shares into common shares.

"Inflation continues to be a tough adversary," said Geico Chairman John J. Byrne. "Operating earnings are down slightly, and net income is off 26 percent. On the other hand, earnings per share (fully diluted) are up nicely, and I am cautiously optimistic that we will be able to manage a satisfactory underwriting gain for the year."