UNC Resources Inc. yesterday reported a second-quarter loss of $6.4 million compared with a loss of $734,000 in the same quarter last year.

The Falls Church-based company attributed most of the quarter's loss to about $7.5 million in expenses incurred in shutting down its uranium mining and milling operations and placing them in a "standby condition" to be reopened should the uranium market recover.

"We will continue to incur expenses in the future to maintain these assets on standby, but at a significantly reduced level," UNC President Keith A. Cunningham said.

Although it reported a wider second-quarter loss than last year, UNC said its revenues more than doubled to $105.1 million, up from $48.1 million in the year-earlier period.

For the first half, UNC reported a net loss of $2.9 million (26 cents), compared with a net profit of $7.5 million (71 cents) last year. Revenues increased to $209.6 million in the January-June period from $144.9 million last year.

UNC, whose major business used to be uranium mining and milling, is a diversified resource and manufacturing company with principal activities in support of the oil and gas industry; manufacture of defense products and machine tools; and exploration for and production of uranium and other minerals.

Peoples Drug Stores posted a 12 percent increase in quarterly profits as the earnings of Washington's biggest drug chain rose to $1.95 million (49 cents a share) from $1.74 million (44 cents) for the three months ended July 3.

Sales for the company's third quarter were up 10 percent to $158.8 million from $143.8 million and for the first 40 weeks of fiscal 1982, People's volume totaled $525.6 million against $491 million in the same period a year ago.

Earnings for the year so far amounted to $7.6 million ($1.90) against $6.8 million ($1.77) in the first three quarters of 1981.

Chairman Adrian C. Israel said the increased earnings resulted because Peoples was able "to obtain a greater share of market" even "within this recessionary economy."