UNC Resources, a Falls Church firm that is the nation's largest independent producer of uranium, reported yesterday a decline in first-quarter profits.

President Keith Cunningham also forecast a disappointing second quarter, but said the current weak performance would be followed by "a substantial improvement" in the second half of UNC's fiscal year.

UNC, the holding company for United Nuclear Corp., listed profits of $6.1 million (57 cents a share) in the quarter ended June 30 compared with $7.5 million (68 cents) in the same period last year. Sales rose to $70.9 million from $68.2 million.

Cunningham said first-quarter earnings reflect the scheduled completion during the first half of the fiscal year of uranium deliveries under earlier, low-priced contracts.

Results in the current quarter will be penalized by the loss of uranium production from one plant because of repairs, he added.

Substantial losses were incurred during the first quarter in starting up UNC Recovery Corp. in Florida. In addition, mechanical problems curtailed coal shipments from UNC Plateau Mining in Utah. Gains in other operations - including increased uranium production - partially offset the negative factors, Cunningham said.

Baltimore Gas and Electric Co. reported profits of $69 million ($1.92 a share) in the first six months of 1979 compared with $68 million ($1.91) a year earlier. Revenues rose to $525 million from $488 million.

A new two-level electric rate structure started last January lowered revenues in the winter months but will boost them during the summer. Sales of electricity rose 7 percent in the first half of the year.

Smithfield Foods Inc., a Virginia meat prodducer, reported second-quarter profits of $563,000 (24 cents a share) compared with $395,000 (16 cents) a year ago as sales rose to $49 million from $39 million.

"Substantially improved fresh meat [gains] were largely responsible for the increased net income," said Chairman Joseph Luter III. Directors also authorized the purchase of up to 100,000 shares of Smithfield common shares on the open market.

Crown Central Petroleum, a Baltimore-based oil company, reported sharply higher second-quarter earnings of $13 million ($3.23 a share) compared with $824,000 (20 cents) a year ago. Sales jumped to $230 million from $161 million.

Equitable Bancorporation, a Baltimore-based bank holding company, reported second-quarter operating profits of $3.6 million (94 cents a share) compared with $3.2 million (84 cents) a year ago. Average loan volume expanded to $1.3 billion in the first half of the year compared with $1.1 billion last year; desposits average $1.7 billion compared with $1.5 billion.

McLean Bank, a Northern Virginia savings institution, reported six-month earnings of $247,420 ($1.47 share) compared with $150.283 (90 cents) a year ago. Deposits on June 30 were $21 million, up 31 percent in the past year. Directors voted a quarterly dividend of 10 cents a share to owners of record June 30.

Chesapeake Corp. of Virginia a pulp and paper manufacturer, reported second-quarter profits of $4.6 million ($1.57 a share) compared with $2.6 million (92 cents) a year ago. Sales rose to $53 million from $41 million.

LogEtronics Inc. of Springfield reported second-quarter profits of $324,000 (31 cents a share) compared with $375,000 (38 cents) a year earlier, which had included an extraordinary credit equal to 11 cents a share.

Not counting the 1978 gain, earnings rose 25 percent as sales increased to a record $7.3 million from $5.7 million. The second-quarter results included revenues and costs for a new laser page scanning and transmission system at The New Yor Times.

Noxell Corp., a Maryland cosmetics firm, said profits rose 31 percent in the first six months of 1979 to $8.4 million ($1.66 a share) from $6.4 million ($1.26) a year earlier. Sales rose to $98.6 million from $84 million.