Dynalectron Corp., a diversified technological services company based in McLean, yesterday decleared a cash dividend despite a 21 per cent decline in profits during 1976.

Earnings totaled $2.5 million (36 cents a share) compared with $3.2 million (46 cents) in 1975, although revenues rose from $176.5 million to a record high of $201.5 million.

In the fourth quarter, Dynalectron's profits also dipped to $500,000 (8 cents) on revenues of $57.4 million from earnings in the 1975 period of $1.2 million (17 cents) on sales of $48.3 million.

Chairman Jorge Carnicero said a number of subsidiaries and divisions experienced reduced profitability because of a "severely competitive business environment," but he noted that the year end backlog of contracts stood at a record $250.2 million, up 122 per cent from a year ago.

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Several major new projects and activities started prior to the end of 1976 had not progressed enough to aid profits strongly "but are anticipated to contribute normal profitability in 1977," the company said yesterday.

Because of the backlog of orders, directors yesterday approved a cash payout of 6 cents a share on common stock and 60 cents on preferred, both payable April 14 to stockholders of record March 30. The local firm declared cash dividents in the three previous years.

Carnicero also reported yesterday that working capital was up 31 per cent last year to $29.5 million, total assets rose 24 per cent to $88 million, and stockholders' equity rose to $29.7 million from $25.2 million in 1975.

Dynalectron divisions are engaged in electrical contracting and construction, support services for government and industry and technology development.