Planning Research Corp. lost a record $1.3 million in the 1981 fiscal year, largely because of the shutdowns of computer system operations in Great Britain and Southeast Asia.

The company, in announcing its results for the year ending June 30, reported a loss of $1.3 million compared with fiscal 1980 profits of $5.5 million (81 cents a share). Sales rose to $314.3 million for the year from $280.8 million for fiscal 1980.

For the fourth quarter, the District company reported a loss of $2.36 million compared with a fiscal 1980 fourth-quarter profit of $1.48 million (22 cents). Sales for the quarter were $82.13 million, up from $81.71 million the year before.

PRC President John M. Toups pointed out that the company's backlog had risen to $296.63 million, an 11 percent increase from the previous year. Toups also said profits of two of the company's branches, Government Information Systems and PRC Engineering, had increased during the year.

"The process of relieving the company of activities that held less promise than the rest of our business has been difficult," Toups said. "Now we're in a position, however, to concentrate on our growth markets and on promising new business opportunities."