American Realty Trust yesterday reported a drop in profits for the Arlington company's third fiscal quarter to $112,446 (5 cents a share) from $196,061 (9 cents) for the same period last year.

Sales for the quarter ended June 30 rose slightly to $1.88 million from $1.79 million last year.

For the first nine months of the fiscal year, the company reported a loss of $23,826 on sales of $4.63 million. During the same period in 1980, the trust reported a loss of $171,287 on sales of $4.5 million.

In another corporate report, United Services Life Insurance Co. reported a rise in second-quarter profits security transactions to $4.7 million (83 cents a share) from $3.7 million (66 cents) last year.

Smithfield Foods reported a first-quarter loss of $727,000 compared with net income of $24,000 (1 cent a share) for the same period last year. The year-ago net income was restated to reflect the change to the last-in-first-out (LIFO) accounting method.

The accounting change increased the loss this quarter by $205,000 and reduced net income a year ago by $238,000, the company said. Sales were $43.5 million compared with $47.3 million.

The decrease in the dollar sales reflected a sharp drop in volume because of a two-week strike by some of the company's workers, the company said. The company also cited increases in live hog costs during the quarter that squeezed profit margins.