Dynalectron, a diversified technological services company involved in industrial construction and electrical engineering, reported relatively flat earnings for the first quarter of 1985.

The McLean company earned $498,000 (5 cents a share) on revenue of $146.7 million for the quarter ended March 28, compared with profits of $493,000 (4 cents) on revenue of $139.4 million in the 1984 quarter.

The company said the 1985 first-quarter earnings were on a reduced number of shares because of the company's buyback program. The effect was to increase earnings per share. The company said flat first-quarter earnings, partly caused by seasonal factors, are typical of the company's experience and not indicative of full-year results.

* Eastmet Corp., a metals manufacturer based in Baltimore, has reported a loss of $6.5 million ($1.30 a share) on sales of $56.2 million for the first quarter ended March 31.

For the same quarter last year, the firm reported a profit of $1.6 million (32 cents) on sales of $70.3 million. That gain included $530,000 on the sale of real estate.

President William F. Dausch said 1985 first-quarter results were adversely affected by the liquidation of inventories but that the effort brought in revenue of about $9.4 million.