CBS Corp, which runs the highest rated U.S. television network, reported a net loss of $55.3 million during the first quarter on sales of $3.16 billion, citing a decline in ad sales amid the current economic downturn. Last year CBS earned $244.3 million.

We are confident that the second half of the year will bring improved results due to a strong slate of syndication releases, the effect of cost reductions that were made last year and early signs of an improving local advertising marketplace,” said Leslie Moonves, chief executive officer of CBS.

CBS earns more than two thirds of its revenue from its Television operations. Television sales were down 12 percent from the same period a year ago, while ad sales fell 15 percent.

Radio sales were down 29 percent to $259.7 million from $363.5 million in the same period last year, also due to a weak advertising marketplace. Operating income fell 62 percent to $43.7 million.

Outdoor sales were down 24 percent to $379.9 million from $496.9 million. It’s Interactive division sales grew to $133.6 million from $52.9 million from the same quarter last year due to the acquisition of CNET. On a comparable basis, revenues were down 5 percent compared to the first quarter of 2008.

Publishing revenues fell 20 percent to $161.7 million from $201.6 million.