Stanwick Corp., an Arlington-based management systems firm, reported earnings of $902,421 (87 cents a share) in the year ended April 30, down from $1.56 million ($1.50) a year earlier. Sales declined to $18 million from $20.3 million.

Both revenues and profits were adversely affected by the Iranian revolution, since Stanwick had to withdraw a majority of employes in that nation who were working on a major contract with Iran's Navy. Costs of the withdrawal and a sharp decline in revenues led to a quarterly loss in the final three months of $753,000 the first loss in nearly six years.

Because of the loss of Iranian business, it will "take some time" to achieve prior revenue through acquistion of new contracts, Stanwick stated.

Neotec Corp., a Silver Spring manufacturer of electro-optical equipment used for agricultural and industrial quality control programs, reported a net loss of $333,340 for the year ended Jan. 31 compared with profits the previous year of $678,000 ($1.51 a share). Revenues also declined to $4.7 million from $5.2 million.

President David Selman, who took over as chief executive on Feb. 1, attributed the unprofitable year to unexpectedly low sales of devices that measure grain quality, an inventory writeoff of obsolete equipment and a requirement to establish a reserve for future warranty expenses.

TransTechnology Corp., a manufacturer of aerospace-defense and textile products, reported a 96 percent increase in earnings for the first fiscal quarter ended June 30. Net income was $321,000 (18 cents a share) vs. $164,000 (9 cents) as sales rose to $7.3 million from $6.5 million.

Tesdata Systems Corp., of McLean, said it expects a loss in the second quarter compared with earnings of $441,000 (35 cents a share) in the 1978 period. The computer performance measurement firm said sales were "below expectations" and less than $4.5 million in the prior quarter. European revenues were off in the 1979 period, president Thomas Stone said.

Commonwealth Natural Resources, a Richmond-based natural gas and energy firm, reported six-month earnings rose to $3.5 ($2.99 a share) from $2.9 million ($1.60). Sales increased to $76 million from $64 million, which the firm attributed to higher product prices and sales volumes.

Regional savings and loan companies reported lower earnings during the first six months of 1979, reflecting the high costs to S&Ls of interest rates for customer savings. Reports from three firms showed:

Providence S&L, of Northern Virginia, had earnings of $471,000 ($2.18 a share), down 13 percent from $546,000 ($2.29) a year ago. Assets rose 14 percent to $125 million and savings deposits were up 12 percent to $111 million.