The Student Loan Marketing Association (Sallie Mae) a private firm that makes a secondary market in guaranteed student loans, has reported a 65 percent increase in first-quarter net income.

Net income was $3.9 million ($3.89 a share) compared with $2.4 million ($2.36) a year earlier. Sallie Mae's assets-- primarily insured student loans purchased and advances outstanding to institutions that participate in the student loan program -- rose to a record $3.3 billion at March 31, an 89 percent increase over $1.7 billion last year.

"The sizable increase in Sallie Mae's income is primarily attributable to increases in demand for the corporation's programs by the lending institutions, state agencies and other organizations that make guaranteed student loans," said Edward A. Fox, president of Sallie Mae.

A. H. Robins of Richmond reported record first-quarter profits of $12.1 million (48 cents a share) compared with $8.9 million (35 cents). Earnings have been restated to reflect adoption in the fourth quarter of the last-in, first-out method of inventory valuation, the company said.

Revenues for the quarter ended March 31 were $114.6 million compared with $104.4 million.

"While we do not expect to maintain the earnings pace of the first quarter, we nevertheless expect 1981 to be one of our best years," President E. Claiborne Robins Jr. said.

The Farmers and Mechanics National Bank of Frederick reported first-quarter earnings of $500,300 (84 cents a share) compared with $460,700 (77 cents). Deposits increased from $208.6 million to $218.8 million, net loans rose from $144.0 million to $146.1 million and total assets increased from $232.7 million to $242.9 million.

Wards Co. Inc. of Richmond reported an 18 percent jump in earnings to $2.7 million ($3.31 a share) from $2.3 million ($2.80) for the fiscal year ended Feb. 28.

Wards owns the Circuit City hi-fi and television stores in the Washington area and sells appliances and consumer electronics goods in a dozen states through its own stores and licensed departments in other retailers' outlets.

Sales of the company increased 10 percent last year to $131.9 million from $119.6 million, but President Alan Wurtzel said sales of existing stores were up only about 2 percent, and most of the total gain came from adding units to the chain.

He said Wards' acquisition of the bankrupt Lafayette Radio Electronics Corp. is proceeding on schedule and is expected to be completed by June.

At W. Bell & Co. sales for the 39 weeks through March 28 increased 10 percent to $82 million from $74.9 million and profits increased to just over $2 million ($1.61 a share) from $1.76 million ($1.41). The per-share earnings were adjusted to reflect a stock dividend.

Sales of the 13 Bell catalogue showrooms climbed 20 percent to $21.7 million from $18.1 million for the 13 weeks ended March 28. The company earned $90,000 (7 cents) during the normally poor quarter compared with a loss of $64,000 last year.