Drug Fair Inc. swung back into the black for the third quarter, reporting a profit of $245,000 (14 cents a share) compared with the $413,000 loss of the previous quarter and earnings of $282,000 (17 cents) in the same period a year ago.

The turnaround for the quarter was not enough to make up for earlier losses, however, and for the first nine months of the year Drug Fair showed a loss of $161,000 (10 cents), down from earnings of $576,000 (34 cents) the year before.

Sales for the quarter were up 5.2 percent -- to $64.1 million from $61 million -- and for the year so far sales are ahead 8.2 percent -- $193 million versus $178.4 million.

Drug Fair President Milton Elsberg said the return to profitability for the quarter shows the chain is "starting to see solid results from our Operation Excellence program," under which 65 stores have been remodeled. The company had earlier blamed the major remodeling and rennovation drive for its loss last quarter and for severely reduced earnings the quarter before.

Radiation Systems Inc. reported 1980 fiscal year first quarter results that showed profits of $162,000 (20 cents), compared to profits of $156,000 (22 cents) for the same period last year.