First Security Corp. reported first-quarter net income of $14.06 million or 92 cents per share, a 9.7 percent increase over the $12.82 million or 85 cents earned in the same period a year earlier.

The regional financial services firm attributed the earnings growth to continued gains in both net interest income and revenues from fee-producing activities and other sources of non-interest income.They were partially offset by increases in the corporation's provision for loan losses and general expenses.

Net interest income was up 8.6 percent to $5.36 million over the first three months of 1990, principally from a 6 percent increase in average earning assets and improvement in the net interest margin.

Growth was also spurred by demand for residential real estate mortgage loans as well as loans to small and middle-market businesses in the Intermountain West, as well as asset growth from acquisitions. The net interest margin rose to 4.58 percent from 4.47 percent a year ago and 4.56 percent in the last three months of 1990.

Non-performing assets totaled $103.31 million at quarter-end, up from $88.58 million a year ago.

The reserve for loan losses was $81.54 million on March 31, up 24.7 percent over the $65.39 million set aside for such contingencies on March 31, 1990, and $80.37 million on Dec. 31.