USAir, the nation's 11th largest airline, reported profits yesterday of $59.1 million ($3.35) for 1982, the second highest earnings in the airline's history.

USAir's record is $60.3 million in 1980.

Net earnings for the year rose 16 percent from $51 million ($3.13) recorded in 1981, while operating revenue of $1.3 billion represented a gain of 15 percent over the $1.1 billion in 1981.

"Against a background of industry losses, our 1982 earnings are extremely gratifying," said Edwin I. Colodny, USAir president.

Fourth-quarter profits were $12 million (66 cents), down 4.7 percent from $12.6 million (73 cents) a year ago, on revenue of $326 million, compared with year-ago revenue of $294 million.

USAir said 16 new jets were added to its fleet in 1982, and 12 more will be delivered in 1983.

Sales during the crucial Christmas season declined 10 percent at W. Bell & Co., the Rockville-based catalogue showroom retailer, but the company posted a 22 percent gain in profits, W. Bell officials said yesterday.

W. Bell sales dropped to $51 million for the quarter ended Dec. 25, from $56 million in the corresponding period of 1981. Profits increased to $1.8 million (90 cents) from $1.5 million (74 cents) in 1981.

Six-month earnings increased to $1.64 million (83 cents) from $1.58 million (80 cents) in 1981. Sales slipped to $73 million from $80 million.

President Walter Bell said fewer promotions leading up to Christmas and a "vigorous cost-reduction program" accounted for the favorable earnings figures.

Last winter was colder than the year before, helping Washington Gas Light Co. increase its 1982 earnings to $21.1 million ($3.41) from $19.2 million ($3.36) in 1981.

Operating revenues at the utility in 1982 grew to $682.8 million from $558 million.

During the final three months of 1982, WGL posted profits of $12.6 million ($2.08), compared with $11.7 million ($2.04) the year before. Revenues increased to $208.4 million from $196.4 million.

Radiation Systems Inc., a Sterling, Va., firm that builds and sells high-tech antennae and related products, posted profits of $1.4 million (48 cents) for the half ended Dec. 31, compared with $1 million (36 cents) in 1981, a 38 percent increase.

Sales jumped 71 percent to $9.5 million from $5.5 million.

Second-quarter profits grew 37 percent to $770,000 (26 cents) from $563,000 (19 cents). Sales soared to $5.4 million from $3 million in 1981, a gain of 82 percent.

The company's backlog of unfilled orders was $21.2 million at the end of the reporting period, compared with $14.8 million the year before.

Union Trust Bancorp, parent of the $1.2 billion Baltimore bank, increased its net income 12.8 percent during 1982 to $11.8 million ($4.80 a share) from $10.4 million ($4.26) in 1981, after securities transactions.

Fourth-quarter profits dropped to $1.9 million (78 cents) from $2 million (84 cents) in 1981.

Before securities transactions, Union Trust had income of $12.8 million in 1982, compared with $13.7 million, and fourth-quarter income was $3.3 million, compared with $3.6 million.

Reduced loan demand and lower interest rates accounted for the bank's decline in earnings in the last quarter, bank officials said.