Washington-based USAir Group Inc. reported third-quarter net profits of $35.1 million, up 46 percent from the $24 million reported during the same period last year.

Earnings per share increased from .04 a year earlier to $1.44.

For the first nine months, USAir showed a net of $92.7 million ($3.83) up 85 percent from $50.1 million ($2.20).

The earnings for the first nine months top last year's total earnings of $80.6 million.

Edwin I. Colodny, chairman and president of USAir Group Inc., said the company's financial base was strengthened by the September sale of $100 million of debentures at favorable rates. Colodny said USAir's cost per available seat mile declined 5.2 percent in the third quarter, which more than offset a 2.9 percent decline in yield. For the year to date, the cost per available seat mile was down 5.8 percent while yield was up 3 percent, he said.

Atlantic Reasearch Corp. reported a 17 percent gain in third quarter profits and a 33 percent improvement in earnings for the first nine months of the year.

The Alexandria maker of rockets and electronic communications gear earned $2.6 million (61 cents) on sales of $47.4 million in the quarter ended Sept. 30, up from profits of $2.2 million (52 cents) on revenue of $34.8 million in the same period a year ago. For the nine months, Atlantic Reasearch earned $7.2 million ($1.71) on revenue of $126.5 million, compared with $2.1 million ($1.29) on revenue of $103 million in the first three quarters of 1983.