Four months into the war, a review of news coverage reveals that over time Americans are getting fewer facts and more opinion — a narrow range of opinion, at that — from newspapers, magazines and television. At the same time, polls show the press losing a measure of the respect it had gained in September, when the public overwhelmingly applauded the timely, comprehensive and informative news coverage it was getting.

The trend away from fact-based reporting is clear in a new study by the Project for Excellence in Journalism, a research institute affiliated with Columbia University and the Pew Charitable Trusts, and Princeton Survey Research Associates. The study examined network, cable and public television; Newsweek, Time, The New York Times, The Washington Post, The Cleveland Plain Dealer and The Fresno Bee; and various TV talk shows. Overall, straight factual reporting dropped to 63 percent of coverage in November and December from 75 percent in mid-September. The remainder of the coverage is analysis, opinion and speculation.

The study also found that the fewer the sources of information consulted in preparing a news report, the more likely it will be filled with opinion and speculation — the very kind of reporting that people consistently tell survey researchers they resent.

Yet despite all the commentary, the range of viewpoints Americans are offered is remarkably limited. Less than 10 percent of the coverage evaluating administration policy offers significant dissent. Most contains no dissent at all.

The findings help explain why polls from the Pew Research Center for People and the Press show only 30 percent of Americans rating the news media’s performance as excellent in mid-November, down from 56 percent in September.

One reason factual coverage declined as the story moved overseas and became more complex is the restrictions — the most stringent in history — that the Pentagon has imposed on the press. Reporters are rarely allowed to be with American troops in the war zones, where they can see for themselves what is happening. We know little firsthand about the risks our soldiers are taking, how well they are equipped and supported and whether they are well led. We know almost nothing about standards of conduct being applied in this new kind of warfare.

This press policy serves no one well. History suggests that the more government restricts press coverage, the less the public is likely to sustain support of a war effort. Pictures of body bags on television did not lead to public disaffection with Vietnam: there were few if any body bags on television. The problem was the government’s deceitful accounting of the war, which led to what popularly became known as the credibility gap.

But it is too convenient simply to blame the Pentagon for the backsliding in coverage. Network cutbacks have left television news hard-pressed to sustain in-depth reporting that keeps up with an increasingly complicated story. Cable networks have substituted talk for reporting. And local newspapers, the study found, have pulled reporters off the story.

It’s interesting that public enthusiasm for the press’s performance began to decline even while the press was overwhelmingly supporting the government. It suggests that citizens intuitively know that the best and most reliable work of the press comes when it is providing independent information.