Dynalectron Corp., the McLean technological services firm with a major entry in the high stakes race for oil-from-coal development, reported yesterday a substantial rebound in profitability during 1979.

In addition, Dynalectron directors voted to make a dividend payment of 8 cents a common share on April 18 to owners of record on April 1. No cash dividends were paid in 1979 although payouts were made from 1974 through 1978, the most recent being 7 cents a share in April 1978.

On the American Stock Exchange, Dynalectron was the fourth most active issue, closing down 25 cents a share to $14.25 on a volume of 240,900. The stock was higher early in the session but eased as the overall market collapsed in late trading. Analysts attributed investor interest in the Northern Virginia firm to an announcement on Tuesdaay that Dynalectron sold an option on its coal liquefaction process to West Germany's largest coal firm for $1 million.

For 1979, Dynalectron's profits were a record at $4 million (57 cents a share) compared with a loss the previous year of $1.5 million. Chairman Jorge Carnicero said all his firm's divisions were profitable as revenues rose to $354 million from $290 million.

In the fourth quarter alone, Dynalectron earned $2.5 million (34 cents) compared with a loss of $500,000 and sales rose to $104 million from $76 million.

Carnicero said Cynalectron's backlog of orders was a record $343 million on Dec. 31, up 41 percent from a year ago. Long-term debt was sliced to $16.8 million from $20.1 million, he added.

In addition to its energy process development, the McLean company is engaged in electrical contracting, technical services for aviation, construction of environmental plants and technology-engineering for chemicals and industrial processes.

Smithfield Foods Inc., a meatpacking firm based in Virginia, reported 1979 profits of $3.5 million ($1.48 a share) from continuing operations compared with $3.85 million ($1.56) from the same businesses in 1978, which included a tax credit of 48 cents a share. Sales rose to $195 million from $171 million.

Preston Trucking Co., a Maryland-based carrier, reported 1979 profits of $6.9 million ($2.19 a share) compared with $7 million ($2.24) in 1978 as revenues rose to $160 million from $145 million.

Tesdata Systems Corp. of McLean said earnings declined to $298,000 (24 cents a share last year from $1.4 million ($1.09) as revenues dipped 7 percent to $15.8 million. Chairman Thomas Stone said the first year-to-year decline in revenues in Tesdata's eight-year history reflected a "basic shift in product and marketing strategy" which did not work out, since it relied on new products that experienced delays in development. These difficulties "are now behind us," he said. The firm supplies computer performance management systems.