Profits plummeted sharply to the break-even level for Dynalectron Corp. in the quarter ended Sept. 30 but rose substantially at UNC Resources Inc. and Flow General Inc., the Washington area companies reported yesterday.

Dynalectron earned a slim $6,000 compared with $1.2 million (17 cents a share) in the same period last year as sales dipped to $73.5 million from $77.7 million.

Following losses in the first and second quarters, the third-period results added up to a nine-month net loss of $987,000 compared with earnings of $1.06 million (14 cents), although sales rose to $214 million from $202 million.

The diversified McLean electrical contracting energy and technical services company said earnings in these primary business lines largely were offset by continued losses under waste water treatment plant construction contracts.

Electrical contracting was profitable following managerial changes and major contracts in recent months are expected to help the group's efforts to return to "more reasonable" profit levels. "However, during the third period, earnings accrued from these new awards were minimal and profits were substantially under budget," the company added.

As for the water treatment plants, Dynalectron has placed them in a new environmental group for "greater management concentration," along with industrial insulation subsidiaries. Overall company contracts at the end of the quarter were a record $269.5 million compared with $244 million a year ago.

UNC Resources, of Falls Church, reported profits in the second quarter ended Sept. 30 rose 37 percent to $9.6 million (88 cents a share) compared with $7 million (67 cents) a year earlier as revenues increased 33 percent to $70.7 million.

The holding company for United Nuclear Corp., a uranium and coal mining firm, UNC posted six-month profit of $1-million ($156) vs. $13.5 million ($1.28) as revenues increased to $139 million from $110 million.

UNC also announced completion of the sale of 600,000 pounds of uranium concentrate for $26 million. The uranium was borrowed from an unaffiliated third party and will be repaid during calender years 1981 through 1983, at which time proceeds will be reflected in earnings and sales.

Flow General, a McLean services firm and manufacturer of biological and broadcast products, reported a 56 percent increase in earnings for the first fiscal quarter ended Sept. 30. Net income was $478,000 (30 cents a share) compared with $307,000 (20 cents) as sales rose 18 percent to $13 million.

NUS Corp., a Rockville energy and environmental consulting company, reported third-quarter profits of $707,000 (71 cents a share) compared with $451,000 (45 cents) a year ago as sales rose to $11.5 million from $9.3 million. Nine-month earnings were $1.9 million ($1.95) vs. $969,000 (97 cents) and sales rose to $33.6 million from $24.9 million.

Penril Corp., a Rockville supplier of data communications equipment, posted record sales and earnings in the year ended July 31. Net income rose 32 percent to $1.2 million (91 cents) from $893,394 (70 cents) on an increase in sales of 40 percent to $14 million.

Log Etronics Inc., a Springfield technology company, reported lower third-quarter profits of $240,000 (23 cents a share) compared with $268,000 (26 cents: a year ago as sales rose to $5.4 million from $4.6 million, Nine-month earning rose substantially, however, to $1 million ($1.02) from $531,000 (53 cents) and sales increased to $16.3 million from $12.15 million.

Wapora, Inc. a Chevy Chase environmental and energy consulting firm, reported profits of $65,333 (11 cents a share) in the first fiscal quarter ended Sept. 30, compared with $22,385 (4 cents) a year ago, as sales rose to $1.4 million from $902,000.

W. Bell & Co., a Rockville catalogue showroom retailer, said profits for its fist fiscal quarter soared 172 percent to $77,300 (8 cents a share) from $28,300 (3 cents) as sales increased 31 percent to $11 million.