We in the news business think we're impartial seekers of truth, but most Americans think otherwise. They view us as sloppy, biased and self-serving. In 1985, 56 percent of the public felt news organizations usually got their facts straight, says the Pew Research Center. By 2002 that figure was 35 percent. In 1985 the public thought the media "moral" by 54 percent to 13 percent; by 2003 opinion was split 40 percent to 38 percent. Americans think the "media make news rather than just report it," says Pew's Andrew Kohut. The obsession with "scandal in high places" is seen as building audiences rather than advancing the public interest.

Still, the latest Pew survey confirms -- with lots of numbers -- an especially disturbing trend that we've all sensed: People are increasingly picking their media on the basis of partisanship. If you're Republican and conservative, you listen to talk radio and watch the Fox News Channel. If you're liberal and Democratic, you listen to National Public Radio and watch "The NewsHour With Jim Lehrer." It's like picking restaurants: Chinese for some, Italian for others. And everyone can punch up partisan blogs -- the fast food of the news business. What's disturbing is that, like restaurants, the news media may increasingly cater to their customers' (partisan) tastes. News slowly becomes more selective and slanted.

Rush Limbaugh has 14.5 million weekly listeners. According to Pew, 77 percent are conservative, 16 percent moderate and 7 percent liberal. Or take Fox's 1.3 million prime-time viewers: 52 percent are conservative, 30 percent are moderate and 13 percent liberal. By contrast, 36 percent of Americans are conservative, 38 percent moderate and 18 percent liberal. The liberals' media favorites are slightly less lopsided. The audience for "The NewsHour" is 22 percent conservative, 44 percent moderate and 27 percent liberal. NPR's audience is 31 percent conservative, 33 percent moderate and 30 percent liberal. Of course, many news outlets still have broad audiences. Daily newspapers are collectively close to national averages; so is CNN.

But the partisan drift may grow, because distrust is spreading. In 1988 Pew found that 58 percent of the public thought there was "no bias" in election coverage. Now that's 38 percent: 22 percent find a Democratic bias, 17 percent a Republican tilt. Almost all major media have suffered confidence declines. Among Republicans, only 12 percent say they believe "all or most" of Newsweek; for Democrats the figure is twice that, 26 percent. In 1985 the overall figure was higher (31 percent), with little partisan gap. Newsweek's numbers typify mainstream media. Only 14 percent of Republicans believe "all or most" of the New York Times, vs. 31 percent of Democrats.

What's going on? Why should we care?

Up to a point, conservative talk radio and Fox represent a desirable backlash against the perceived "liberal bias" of network news and mainstream media. I've worked in the mainstream press for 35 years. Editors and reporters reflexively deny a liberal bias, even though many ordinary people find it and mainstream newsrooms are politically skewed. Here are the latest Pew figures: 7 percent of national reporters and editors are conservative (a fifth the national rate), and 34 percent are liberal (almost twice the national rate). Most reporters I know believe fiercely in being fair and objective. Still, the debate over "what's news and significant?" is warped. Talk radio and Fox add other views.

But the sorting of audiences by politics also poses dangers -- for the media and the country. We journalists think we define news, and from day to day we do. Over the longer run that's less true. All news organizations must satisfy their audiences. If they don't, they go out of business. "Media bias is product differentiation," says James T. Hamilton of Duke University; his book "All the News That's Fit to Sell" shows how economic forces powerfully shape news judgments. If liberals and conservatives migrate to rival media camps, both camps may ultimately submit to the same narrow logic: like-minded editors and reporters increasingly feeding like-minded customers stories that reinforce their world view.

Economic interests and editorial biases will converge. The New York Times is now a national paper; 49 percent of its daily circulation is outside the New York area, up from 38 percent five years ago. There's home delivery in 275 markets, up from 171 five years ago. But if the Times sells largely to upscale readers (average household income is $90,381, almost twice the national average) with vaguely liberal views, it risks becoming hostage to their sensibilities. No less does Fox risk becoming hostage to its base.

The worthy, if unattainable, ideals of fairness and objectivity will silently erode. Many forces push that way: new technologies (cable, the Internet); the blending of news and entertainment; the breakdown between "hard news" and interpretation; intense competition; changing news habits of the young. The damage will not just be to good journalism. Tom Rosenstiel of the Project for Excellence in Journalism notes that respected national media develop common facts and language that help hold society together and solve common problems. It will be a sad day when we trust only the media that voice our views.