Dynalectron Corp. of McLean reported second-quarter profits of $787,000 (11 cents a share) yesterday, a total which the company called "a marked contrast" to last year's loss fo $572,000 (9 cents).

The second quater's earnings pushed Dynalectron's profits for the first half to $989,000 (14 cents) compared with losses of $993,000 (15 cents) a year eariler.

For the three months ended June 2, Dynaletron reported revenues of $86.9 million, up from $73.6 million; first-half revenues climbed to $162.1 million from $140.5 million.

A year ago, Dynalectron's electrical contracting division was showing heavy losses, which depressed the company's earnings.

Washington Gas Light Co. reported its earnings for the 12 months ended June 30 fell by $961,000 to $11.3 million from $12.3 million, as revenues slipped from $353 million to $351 million.

Earnings per share declined from $2.84 to $1.60, but $1.01 of that amount was due to a change in accounting methods.

Restating the gas company's earnings to show the impact ot the accounting change produced d net profit for the period of $11.8 million, down from $15.9 million, and common stock earnings of $2.06, down from $2.98.

American Management Systems of Arlington reported its earnings increased to $390,000 (27 cents a share) from $177,000 (16 cents) for its second quater, while revenues climbed to $11.6 million from $7.3 million.

AMS' earnings for the first half totaled $768,000 (57 cents), up from $308,000 (28 cents); revenues were $21.9 million against $13.2 million. CAPTION: Chart, Big Oil Profits, By Alice Kreese- The Washington Post