UNC Resources Inc. of Falls Church yesterday reported a smaller fourth-quarter loss than last year but also smaller annual earnings, and company officials said the numbers are confused by accounting changes and don't fully reflect recent changes in UNC's operations.

For the quarter, UNC lost slightly more than $1 million on revenues of $65.6 million compared with a loss of $1.9 million on revenues of $49.1 million last year.

The calendar year produced a profit of $6.9 million (65 cents a share) from revenues of $277 million. UNC previously used a fiscal year ending March 31. In the last year under that calendar, UNC made $17.4 million ($1.64) on revenues of $302.6 million.

President Keith Cunningham said results for the two years were not directly comparable because of the different periods involved and gains from the sale of subsidiaries and mineral rights that produced windfall earnings in both periods. UNC's 1981 profits included a $7 million pretax gain from the sale of assets, while the previous fiscal year's results included a $36 million profit from such sales.

"The calendar-year figures do not yet reflect the changed character of the company," Cunningham added. "They include results of National Automatic Tool Co. and Normco Contractors only since their acquisition in midyear and do not include any results of Swiftships Inc., a major acquisition which took place last month." Blaming the fourth-quarter loss on nonrecurring write-offs, Cunningham said "we expect to be profitable in the next quarter and in the calendar year.