Baltimore Gas and Electric Co. reported increased earnings for the first half of the year despite a slump in business activity affecting major BG&E customers.

But for the Stanwick Corp. and Software AG Systems Group Inc., last year wasn't a banner year. Stanwick posted losses, and profits declined significantly at Software AG, officials for the Northern Virginia companies reported.

BG&E said that net income for the first six months of 1982 was $83.9 million ($1.99 a share) compared with $74.9 million ($1.89) for the first half of 1981. Second-quarter earnings were $38 million (86 cents) compared with $31.4 million (74 cents) for the same quarter in 1981.

BG&E said that kilowatt-hour sales of electricity were slightly lower in the first half of 1982 than they were in 1981, but the total volume of gas sold increased 1.1 percent. The utility said that sales of both types of energy had been affected adversely by the reduced level of business activity, particularly in the steel industry.

Total operating revenues in the first half of 1982 were $829.3 million compared with $698.6 million in the first half of 1981. For the quarter they were $366.1 million compared with $314.2 million in 1981.

Stanwick, a supply management and engineering services company in Arlington, had 1982 losses of $1.3 million on revenues of $13.2 million, compared with 1981 losses of $639,242 on revenues of $19.8 million for the fiscal year ended April 30.

Stanwick officials cited a "dramatic decline in its technical support services business"--tradespersons and technicians for the shipbuilding and repair industries--closing of a repair division and provisions for tax losses in California for the growing losses. Officials pointed out, however, that Stanwick had an "adequate amount of working capital" and no short-term debt.

Software AG of Reston posted annual earnings of $1.2 million (20 cents a share) for the year ended May 31, compared with $2.3 million (50 cents) in 1981.

Revenues during that time grew to $24 million from $18.9 million. Operating costs associated with expansion and uncollectable accounts were cited as causes for the declining earnings.