Allegheny Beverage Corp. of Cheverly, Md., reported a third-quarter loss of $594,000 (-9 cents a share), compared with earnings of $3.4 million (52 cents) during the same period last year.

The firm said its revenue for the third quarter ended Dec. 31 was $130.6 million, compared with $96.9 million during the same quarter last year.

Earnings for the nine months dropped to $4.8 million (73 cents), compared with $9.2 million ($1.42) for the same period in 1983.

Allegheny Beverage attributed most of the decrease in earnings to higher interest costs related to its floating rate debt. "Other unusual expenses in the 1984 period were incurred in connection with the computer conversion at our office furniture subsidiary and on a major closeout of electronic game operations," said Morton M. Lapides, president of the firm.

Bowl America Inc., a Springfield-based bowling company, said its earnings for the second quarter climbed 1.2 percent to $583,908 (37 cents) on revenue of $4.8 million, compared with $576,768 (36 cents) on revenue of $4.67 million during the same period last year.

For the first six months, the firm said its earning rose 2.4 percent to $528,169 (33 cents) from $515,731 (32 cents) during the same period last year.

E.C. Ernst Inc., an electrical construction contracting firm in Fairfax that has been operating under the protection of Chapter 11 of the Federal Bankruptcy Code since 1978, reported its third-quarter earnings were $59,000 (1 cent) on revenue of $14 million, compared with a loss of $3 million on revenue of $14.1 million during the same period last year.

For the first nine months, the company lost $9.35 million on revenue of $37.4 million, compared with a loss of $7.5 million on revenue of $41.9 million during the same period in 1983.

United Savings Bank in Vienna said its third-quarter earnings rose 90 percent to $377,000 (78 cents), compared with $198,000 (57 cents) during the same period last year.

United Savings reported its annual earnings climbed 68 percent to $1.27 million ($3.32), compared with $756,000 ($2.16) during the same period last year.

The bank also announced that its assets grew by 48 percent to $233 million, up from $157 million at the end of 1983.

Systematics General Corp., a Sterling, Va., firm that provides systems engineering services to the federal government and computer terminal manufacturers, said that its fourth-quarter net income dropped 43 percent to $392,000 (14 cents) on sales of $7 million, compared with $692,000 (25 cents) on sales of $6.9 million for the same period last year.

For the year, the company reported its net income rose 1 percent to $1.729 million (64 cents) from $1.7 (63 cents) million for the previous year.

Sales for the year soared 40 percent to $29.5 million, compared with $21 million in 1983.

Bernard Farkas, president of the company, said that delays encountered in the fourth quarter with a large customer contract prevented the company from maintaining its profit growth rate.

Genex Corp., a Rockville biotech firm, announced a fourth-quarter loss of $7.5 million (59 cents) on revenue of $1.3 million, compared with a loss of $1.7 million (13 cents) on revenue of $4.7 million for the same period in 1983.

For the year, the company reported a loss of $7.4 million (58 cents) on revenue of $34.8 million, compared with a loss of $5.4 million (43 cents) on revenue of $11.1 million for 1983.