Americans are not reading newspapers so much any more, and newspaper people are wondering what to do about it.

At its annual convention here, the American Newspaper Publishers Association distributed a cheerful little pamphlet, full of news about increased advertising and Sunday sales but omitting one stark fact:

In the last three decades the number of newspapers sold in the United States has fallen behind population growth. In 1950, one daily paper circulated for every 2.8 Americans. Today the ratio is about one paper for every 3.6 persons.

Although their pamphlet failed to mention this, the publishers and their guest speakers brought it up often, focusing on the competition for readers' attention from cable television, home computers, mailed advertising and specialty magazines.

"The decline that has taken place in household penetration of newspapers leaves us vulnerable," said Washington Post Co. president and outgoing ANPA president Katharine Graham. Former newspaperman and now screenwriter Kurt M. Luedtke, speaking as a reader, said bluntly: "We don't need you quite as much as you tell us we do."

At one packed session on "successful newspapering in the 1980s," editors, publishers and a public opinion expert tried to suggest cures for the troubling reader disenchantment. Some suggested small measures--Detroit Free Press executive editor David Lawrence Jr. said one editor advised just stopping by after work to share a beer with the boys at the local gas station.

But Luedtke, who wrote the movie "Absence of Malice," suggested a complete reappraisal of some of American journalists' most cherished beliefs.

By using unnamed sources, Luedtke said, reporters were simply denying a man's right to confront his accusers. He said newspapers might have been better off if the Supreme Court had never given them the right to criticize famous people without fear of a libel suit. The political news which newspapers spend so much time and space on "looks like news, . . .feels like news, and nobody reads it."

Many of the publishers at first seemed stunned by Luedtke's frontal assault, but copies of his remarks were in demand the rest of the session.

"There is no such thing as the public's right to know," Luedtke said. "You made that up, taking care not to specify what it was that the public had a right to know. The public knows whatever you choose to tell it, no more, no less. If the public did have a right to know, it would then have something to say about what it is you choose to call news.

"If you search through your newspaper for information that the reader can actually act upon, you will find very little of it that isn't advertising. There is the TV book, the weather and the food pages; at most newspapers, that's pretty much it," he said.

The former Detroit Free Press executive editor, whose movie was a fictional account of a ruined career and a suicide caused by newspaper stories, questioned the notion that newspapers can disregard criticism from politicians, bureaucrats and businessmen because they are seeking reader favor. He also suggested that editors feel criticism from readers can be disregarded because they don't understand how newspapers work.

Robert C. Maynard, editor of the Oakland Tribune and Eastbay Today and a former Washington Post ombudsman, said he gleaned from conversations with editors throughout the country suggestions that newspapers should explain how they work. One editor said his paper distributed "a graphic booklet on how to write a press release for his newspaper," Maynard said. "Some hold seminars for publicity chairpersons."

Maynard said the New Bedford (Mass.) Standard-Times has sent a questionnaire to people who had been mentioned in the paper, asking if the stories were fair and accurate. Although reporters were not happy, the stories' accuracy rating climbed from 88 per cent to 92.6 percent in two years, fairness rose from 95 percent to 97 percent and completeness went up from 78 percent to 84.4 percent.

"It is a personal opinion of mine," Luedtke told the editors, "that reporters really don't realize how inaccurate they are simply because they assume, as I must say I would, that a story is correct until someone complains. Left out of that equation are all of those who don't want to make waves or who are afraid of offending you or who don't know how or who cool down and don't bother or who are brushed off by whoever answers the phone. Call your city desk anonymously some time and see if you like the feeling."

Maynard agreed. He recalled that one Washington Post editor once ended a telephone conversation by saying: "Madam, if you persist in this manner I will have no choice but to cancel your subscription.".

Some editors told the publishers they had to increase the range of stories they offered. Luedtke recommended more "how to" stories. Lawrence presented a long list of ideas from stories that would give more of a sense of the past in the newspapers circulation area to regular listings of programming on cable television.

Ruth Clark, of the public opinion firm of Yankelovich, Skelly and White, Inc., said editors must recognize three important differences in readers of the 1980s--they are generally older, more concerned about jobs and money and less interested in experiments in changing social values that intrigued readers in the 1960s and 1970s.