Vega Precision Laboratories, a Vienna manufacturer of radar tracking and control systems, has reported a 40 percent gain in earnings during 1977.

Profit totaled a record $396,793 ($1.04 a share) compared with $284,189 (74 cents) in 1978 as sales increased 23 percent to $9.2 million, D.M. Kruchtko said Vega currently has a backlog of orders that exceeds $9 million. He projected an increase in the growth of sales and profits during 1978, partially from development of new products.

YPenril Corp., a Rockville supplier of data communications equipmnent, reported record profits of $616,187 (48 cents a share) in the six months ended Jan. 31, compared with $375,981 (30 cents) a year earlier. Sales increased 41 percent to $6.6 million.

President Kenneth M. Miller said that, as a result of earning growth, directors voted a 100 percent increase in Penril's semi-annual cash dividend. A payout of 5 cents a share will be distributes May 15 to owners of record April 28.

Preston Tracking Co. reported a 13 percent decline in profits last yeat despite an 11 percent increase in revenues. The Marylnd trucking firm's profit were $6.6 million ($210 a share) in 1976. Sales increased to $122 million from $110 million.

The earning decline was attributed to bad weather conditions early in 1977 and in meeting challenges to acquisition of Shippers Dispatch Inc., last year. Directors voted a dividend of 121/2 cents a share payable April 14 to owners of record March 31.

Second National Building and Loan Inc., of Ocean City, reported record profits in 1977 o $360,028 ($3.88 a share) compared with$274,227 ($3.01) the previous year. Assets increased by 60 percent to $55 million. Second National has offices in Salisbury, Easton and Annapolis; a branch application for a Cambridge office is pending.

Alleghency Airlines of Washington, in a monthly earnings statement, reported a February loss of $2.6 million compared with a loss of $4.3 million in the same year. Revenues rose to $36 million from$32 million. Allegheny said traffic was strong during the first half of March and, if current traffic trends continue, that the month should be profitable compared with a loss last year of $354,000.