Ameribanc Investors Group, parent of Ameribanc Savings Bank of Annandale, yesterday reported a 12.7 percent increase in profits for the second quarter, ending June 30.

Ameribanc said its net income rose to $2.2 million (34 cents a share) from $1.9 million (32 cents) in the comparable quarter of last year. For the first half of the year, the thrift institution reported profits rose to $4.4 million (68 cents) from $3.7 million (62 cents) a year ago, for an increase of 18.3 percent.

William H. Savage, president and chief executive officer of Ameribanc Investors, said that second quarter results included the writeoff of a $126,000 secondary reserve required by the Federal Savings and Loan Insurance Corp.

Kay Jewelers Inc. yesterday reported a net loss of $492,000 (6 cents) on revenue of $73.2 million during the second quarter ending June 30, compared with profits of $390,000 (5 cents) on revenue of $54.0 million last year.

For the six months, the Alexandria-based jewelry retail chain had a loss of $3.9 million (49 cents) on revenue of $132.6 million, compared with a loss of $775,000 (10 cents) on revenue of $95.7 million during the same period last year.

The increase in revenue between 1986 and 1987 was largely a result of the acquisition of J.B. Robinson Jewelers, the company said.

Washington Gas Light Co. reported that the net loss applicable to common stock was $6.3 million (37 cents) on revenue of $104.7 million for the second quarter ending June 30, compared with a loss of $3.9 million (23 cents) on revenue of $108.2 million for the same period last year.

For the first half of the year, income was $29.2 million ($1.74) on revenue of $411.8 million, compared with profits of $27.5 million ($1.67) on revenue of $438.3 million in the previous year.

Hadron Inc., of Fairfax, a professional services company, reported a 53.7 percent increase in profits on a 28.1 percent growth in revenue for its first quarter, ending June 30. Hadron's sales rose to $6.7 million from $5.2 million in the same period a year ago. Net income rose to $384,036 (3 cents) from $249,859 (2 cents)