Suffolk Bancorp said Thursday it was able to make a profit in the third quarter mostly because it didn't have to add money to its fund for loan losses.

The Riverhead-based parent of the 28-branch Suffolk County National Bank also cited higher noninterest income and lower operating expenses in reporting net income of $3.9 million, or 34 cents a share, in the three months ended Sept. 30.

A year earlier it reported a net loss of $9.2 million, or 94 cents a share, which it blamed on the addition of $12 million to its fund for loan losses, known in banking as an "allowance" for loan losses.

The allowance stood at $17.6 million as of Sept. 30, the bank reported.

In this year's quarter, Suffolk said it added no money to the fund, while noninterest income rose by 250 percent to $6.6 million and operating expenses fell 12 percent to $15 million.

Partially offsetting these factors was a 13 percent reduction, to $13.9 million, in net interest income in this year's third quarter.

The company's net interest margin, a measure of the difference between the interest a bank earns on its assets, such as loans, and the interest it pays out to depositors, narrowed 27 basis points to 3.82 percent.

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President and chief executive Howard C. Bluver said in a statement, "We remain well ahead of our internal projections for the overall business as we approach the end of 2013."

Total assets at the end of the quarter were $1.7 billion, up 10 percent from a year earlier.

The bank closed two branches Oct. 4, in Middle Island and in Water Mill.

Loans outstanding at Sept. 30 increased by 30.4 percent to $999 million from a year ago.

Shares of Suffolk Bancorp rose 3 cents to close at $19.59.