Alleco Inc., the former Allegheny Beverage Corp., yesterday reported quarterly results that were the first to be affected by the sale of its major subsidiary, Service America Corp.

The Cheverly company, which now is a cash shell looking for other businesses to buy, said that a $27.9 million gain was realized on the $345 million sale of Service America to Servam Corp. on Dec. 2. In addition to the cash paid to Alleco, Servam assumed the cash liability on $105 million worth of 9.5 percent debt.

For the quarter ended Dec. 26, Alleco said earnings were $20.3 million ($2.38 a share) on sales of $2.04 million. For the same 1986 quarter, the company lost $42.8 million on sales of $356,000.

For the nine-month period, Alleco had earnings of $11.1 million ($1.30) on sales of $2.5 million. That compares with a $53.4 million loss ($6.25) on sales of $1.9 million for the same period in 1986.

Fairchild Industries Inc. said it earned $23.1 million (82 cents) in 1987, compared with a $10 million loss ($1.58) in 1986. Revenue rose to $453.8 million from $448.8 million, the Chantilly-based defense contractor said.

The company, which has been undergoing a major restructuring, said its earnings from continuing operations during the year were $11.5 million (6 cents), compared with a $4.1 million loss on continuing operations a year ago.

Fairchild's fourth-quarter profit was $500,000, which translated to a 12-cent loss per share after the company's preferred stock dividend was paid. A year ago, the company lost $73.6 million in the fourth quarter. Revenue rose 11 percent in the quarter to $123.2 million from $111.5 million last year.

Smithfield Foods Inc. said its earnings more than doubled in the third quarter that ended Jan. 31, to $9.2 million ($2.09) from $4.3 million (95 cents) a year ago. Sales, however, dipped to $234.5 million from $291.4 million.

In the first nine months of the year, earnings rose to $13.6 million ($3.01) from $6.7 million ($1.50) a year earlier, when the results included a $2.1 million loss due to the retirement of some debt. Nine-month sales fell to $723.5 million from $816.9 million.

The meatpacker said sales fell in the quarter and nine-month periods because of lower prices on its products resulting from lower raw material costs, and because of a sharp drop in sales by its Wisconsin-based Patrick Cudahy Inc. division, which ended slaughtering operations and filed for bankruptcy protection late last year after a labor dispute.

Hadron Inc., a Fairfax-based computer software and professional services company, said it earned $302,021 (2 cents) in its third quarter ended Dec. 31, down 10 percent from $333,979 (2 cents) a year ago. Revenue in the quarter fell 10 percent, to $6.3 million from $7 million.

In the first nine months of the year, Hadron earned $1 million (7 cents), up 14 percent from $892,020 (7 cents) a year ago. Revenue in the nine months rose 8 percent, to $19.7 million from $18.3 million.

Capital Bank N.A. of Washington said it earned $617,000 ($2.47) in 1987, up 17 percent from $528,000 ($2.64) in 1986. Per-share figures were lower last year because more shares were outstanding.

The bank said it earned $171,000 (68 cents) in the fourth quarter, up 8 percent from $158,000 (63 cents) a year ago.

Assets at the end of 1987 were $77 million, compared with $76 million at the end of 1986.

Micros Systems Inc., a Beltsville-based maker of electronic cash registers and related equipment and software, said it earned $58,100 (1 cent) in the second quarter ended Dec. 31, compared with a $199,900 loss in the quarter a year earlier. Revenue rose to $4.95 million from $4.87 million.

In the first half of its fiscal year, Micros Systems earned $136,000 (2 cents), compared with a $439,300 loss in the period a year ago. Revenue rose to $9.9 million in the half from $8.9 million last year.

Biospherics Inc., a Rockville-based research firm, said it earned $452,052 (12 cents) in 1987, up 46 percent from $309,455 (8 cents) in 1986. Revenue increased 32 percent, to $10.5 million from $8 million.

In the fourth quarter, Biospherics earned $29,907 (no dividend), down from $40,180 (no dividend) a year earlier. Revenue in the quarter rose 33 percent, to $3 million from $2.3 million.