U.S. Health Inc. of Baltimore, a holding company that operates Holiday Spas and other sports and fitness facilities, reported a small gain in gross operating revenue and a drop in net income and per-share earnings for the quarter ending Jan. 31.

Gross operating revenue climbed from $19 million to $20 million, while net income fell from $2.8 million (54 cents) to $2.3 million (45 cents). For the six months ending Jan. 31, gross operating revenue rose from $27.7 million to $31.5 million, but net income fell from $3.4 million (65 cents) to $3.1 million (60 cents.)

* Baltimore Gas & Electric, reporting that mild weather trimmed electric and gas sales during January, said it earned $15.3 million in common-stock earnings (39 cents), compared with $23 million (59 cents) during the same month in 1984. For the 12 months ended Jan. 31, BG&E earned $208.5 million ($5.33 cents), compared with $197.8 million ($5.17) in the previous year.

* United Dominion Realty Trust of Richmond reported that cash flow from operations increased to $374,000 (22 cents) from $322,000 (22 cents) for the quarter ending Dec. 31. Net income for the quarter was $254,000 (15 cents), compared with $158,000 (10 cents) for the previous year.

For the year ending Dec. 31, cash flow from operations increased to $1.4 million (87 cents) from $1.1 million (81 cents). Net income was $2.7 million ($1.62), compared with $1 million (70 cents). The results include only the operations of Old Dominion Real Estate Investment Trust, which merged with Realty Industries on Dec. 31.

* Crown Central Petroleum Corp. said net income for 1984 was $504,000 (a loss of 12 cents per share), after considering the effect of dividends payable on convertible preferred stock. This compared with a profit of $4 million (44 cents) in 1983.

"This past year was a very rough one for Crown and other independent refiner-marketers," said Crown Chairman Henry A. Rosenberg Jr., because of the "severe imbalance between crude oil and refined product prices." The company had a loss from continuing operations for 1984 of $6.8 million ($1.28), compared with a profit of $1.6 million (6 cents) for 1983.