In the last decade, 150 newspapers in the United States have ceased operating. Dallas now joins the ranks of cities like Los Angeles, St. Louis, and Cleveland that have just one major newspaper. Within the past two months, papers in Arkansas and Tennessee have folded. In New York, the Daily News, owned by the late Robert Maxwell, has declared bankruptcy.Media-watchers cite trends for the difficulties facing the industry: decline in readership and competition for advertising from broadcast and now cable services. And the recession has eroded advertising spending generally. This year it will decline for the first time in 30 years and by the largest percentage in 50 years, according to projections made by McCann-Erikson at a media conference last week.