USAir Inc.'s profits in the first 10 months of 1980 were nearly double those of the previous year, and October was the most profitable month in the company's history, the Washington-based airline reported.

Net income for the year, through October, rose to $51.7 million ($4.06 a share) from $27.9 million ($2.23) as revenues soared 35 percent to $798 million.

In October alone, USAir earned $9.6 million (77 cents) on revenues of $94 million compared with earnings in October 1979 of $3.6 million (28 cents) on revenues of $69 million.

Potomac Electric Power Co. listed earnings of $95 million ($1.96 a share) for the 10 months ended Oct. 31 compared with $73 million Oct. 31 compared with $73 million ($1.53) in the same period last year. Revenues rose to $729 million from $639 million.

Crown Central Petroleum Corp. reported a steep drop in third-quarter profits to $398,000 (1 cent a share) compared with $22.9 million ($4.28) for the same quarter last year. Sales for the quarter were $317.7 million, compared to $282.2 million for the 1979 third quarter.

For the first nine months of the year, the Baltimore petroleum firm's profits have fallen from $52.23 million ($9.74) to $15.27 million ($2.37). Sales, however, rose to $953.1 million for the first three quarters, compared with $727.5 million for the same period in 1979.

Biospherics Inc., a Rockville environmental controls firm, reported a loss of $18,182 for the first nine months of the year, compared with profits of $225,168 (16 cents) for the same period in 1979. The company's revenues rose this year to $4.41 million from $3.63 million in 1979.

Systematics General Corp. reported third-quarter profits of $111,000 (7 cents a share), compared with a loss of $226,000 for the same quarter last year. Sales for the third quarter for the Falls Church company rose to $2.8 million, from $1.9 million.

For the first nine months of the year, the company reported profits of $613,000 (45 cents), compared with a loss of $726,000 for the same period last year as sales rose to $8.3 million from $5.4 million.

Computer Network Corp. reported a third-quarter loss of $74,000 compared with a third-quarter profit of $360,000 (22 cents a share) last year. Sales for the quarter dropped to $5.1 million from $5.6 million.

For the first six months of the fiscal year, the company reported a loss of $192,000 compared with profits of $650,000 (40 cents) for the same six months last year.

Arundel Corp. of Baltimore reported a third-quarter loss of $7.69 million compared with profits of $372,000 (20 cents a share) for the 1979 third quarter.The company reported a nine-month loss of $8.68 million compared with profits of $2.96 million ($1.75) fo the same period last year.

BTR Realty Inc. reported a drop in profits for the first three-quarters of the fiscal year, as profits fell to $345,146 (63 cents a share), compared with profits of $453,589 (83 cents) for the same period in 1979. Revenues for the Linthicum Heights, Md., company rose to $3.23 million, compared with $2.67 million in 1979.

HGIC Corp. of Richmond, the parent company of Home Guaranty Insurance Corp., reported third quarter earnings of $98.487 (10 cents a share), up from $67,413 (7 cents) last year. Revenues for the period were $56,605, up from $504,202.

Nine-month net income was $221,918 (23 cents), compared with $185,072 (19 cents), while revenues were $1.6 million, compared with $1.4 million in 1979.

Bowl America, a Springfield bowling centers operator, posted a loss of $85,813 in its first quarter, ended Sept. 28, compared to a loss of $57,650 in the same period in 1979. Bowling centers normally operate at a loss during the summer months. The company's revenues rose to $2.84 million, from $2.75 million.