CHICAGO – Tribune Co.’s steady decline in revenue accelerated in May on a 12 percent drop in advertising revenue, the media conglomerate said Wednesday.

The company said revenue for the month was $406 million, down 11 percent from $457 million a year earlier. The decline was three times the rate of April’s year-over-year drop.

Decreases came across the board in all businesses owned by Tribune, which is awaiting final approval of an $8.2 billion transaction taking it private by year’s end under the leadership of real estate investor Sam Zell.

Revenue from its publishing or newspaper division fell 10 percent to $292 million from $325 million in May 2006 and revenue from the broadcast and entertainment group was down 13 percent to $114 million from $131 million.

Television revenue slid 11 percent, with lower automotive, movie and political advertising partially offset by strength in retail and telecom/wireless categories. Tribune said the results also reflected fewer Chicago Cubs home games in the latest period versus last year.

Advertising revenues decreased to $230 million from $261 million. Retail ad revenue slid 1 percent, while national advertising revenue dropped 17.9 percent.

Classified ad revenue tumbled 20 percent, with real estate dropping 30 percent on significant declines in the Florida, Chicago and Los Angeles markets.

Circulation revenue skidded 6.2 percent on lower single-copy sales and selective discounting in home delivery.

Tribune owns 11 daily newspapers, 23 TV stations and the Cubs.

Shares in the company fell 46 cents or 1.5 percent in after-hours trading after closing the regular session down 35 cents at $29.96.