Craig Ammerman takes his own survey daily. He leaves his office, walks to a newsstand in downtown Philadelphia, intently watches who buys what and, more important, who doesn't.

It's those people who pass the papers by, many of them women, that are critical. Ammerman needs them to survive.

He's the editor of The Philadelphia Bulletin, once the largest evening paper in the nation and a pillar of Philadelphia with an unassailable economic position. For generations its motto, "In Philadelphia, Nearly Everybody Reads the Bulletin," was more reality than boast.

Now they don't. More than 300,000 readers have stopped buying the Bulletin. These days, the paper desperately struggles to get enough of them back to stay in business.

It won't be easy. Some insiders there put the odds of survival at no better than 25 percent.

In New York, similar grim battles are being waged to win vanishing newspaper readers, and not only in the familiar afternoon field now littered with the corpses of once-prosperous dailies. The morning New York Daily News, the largest circulation American metropolitan daily, which just folded its afternoon paper, Tonight, is itself in trouble.

Something more than newspaper woes are being exposed here. The plague that seems to have descended on major metropolitan daily papers, with shutdowns in Washington and New York, threats of extinction in Philadelphia, talk of further paper mergers in the Midwest, figures recording fewer papers and a total national circulation that has remained stagnant for a generation, are all a commentary on changing American tastes and values.

They offer clues as to why people read, or don't, or can't; what they want to read, and either think they're getting or not; how they spend their leisure time, and what permanent impact television has had on their lives; how important they regard their sources of information, and whether they are satisfied with them.

For most of American history, daily papers provided the essential news upon which citizens formed opinions and reached political judgments. Without grandly overstating the obvious and inflating the press' importance, they have been a vital part of the democratic process.

Newspapers still are a mighty national force. They employ more than 432,000 people and rank first in the Labor Department's listing of the nation's largest manufacturing employers (steel mills, automobile/car body plants and auto parts manufacturers follow them). Their annual advertising revenues of $15.6 billion continue to be more than that of television and radio combined.

Most of the surviving papers remain highly profitable enterprises with promise of even brighter economic futures. But collectively their readership fails to keep pace with the growing American population, and even some of the strongest papers now find themselves in grave trouble. New York's Daily News is a prime example.

In its heyday, when it broke the mold of traditional American journalism, invented the racy tabloid form and prided itself on giving readers exactly what they wanted in superb professional style, The News was printing 2,343,000 papers each morning. Its promotion ads then said:

"Having papers on hand, of course, is not enough. You must also have readers who want them, and buy them as News readers do every day, without subscription contract or carrier boy. The largest newspaper circulation in this country is bought, not sold, every day!"

That was then. In the last generation, 800,000 readers have stopped buying The News. Now some of its own people privately give it only a 50-50 chance of surviving. By its own estimates, this year's losses will run about $11 million, the staff has been slashed, and pay for top executives cut 10 percent.

At the end of Manhattan, literally in the shadow of the Brooklyn Bridge and a stone's throw from old Park Row where the dominant papers of the nation once were housed, another kind of search for readers takes place daily.

"We take very, very careful note of what we do," says Steve Dunleavy, metropolitan editor of The New York Post, a tabloid that now publishes around the clock.

"We watch who's buying the paper and why. I see who's reading the paper on the subway, and what they're reading. We get feedback from our circulation drivers on what sells. We listen to what the people have to say, the straphangers, the policemen and the firemen and their wives.

"The point is, we have a formula, and I know a lot of journalists sneer at our formula, but it works. Our formula is publishing stories that have emotion in them, and we do it with a rifle shot not a shotgun blast. People like to buy something they can feel, something that affects their heart and their pocketbook."

When he arrives at his office, Dunleavy, an Australian like the paper's owner, Rupert Murdoch, quickly moves around the newsroom, chatting briefly with his editors and reporters. "Do you have a baby story?" he asks. "Do you have a dog story? Do you have a heartbreak story?"

They know exactly what that shorthand means. If they don't, they can look at posted past front pages to decipher the formula. One reads:

BABY

LIVED

IN A

BOX!

And, under a streamer line that read, "Reagan Warns Libya:"

WE'D

DO IT

AGAIN

Dunleavy picked up that edition, slapped his hand on a picture of a pensive-looking, dark-haired young woman played next to the Reagan-Libyan headline, and said:

"Now The Washington Post wouldn't have given it that display on Page One, but they'd run it big in their Metro section. That's a good murder."

The story, as the paper told its readers, was about a "coed knifed, left to die in blazing car."

With unintentional irony, a copy of the 100th edition of The Post, preserved in plastic, lay on the desk near Dunleavy. The lead article reprinted recollections of the paper by its most famous editor, a courtly, bewhiskered gentleman better remembered today as the gentle poet William Cullen Bryant.

A stern portrait of one of the paper's founders was printed alongside Bryant's history. It was of the arrogant intellectual, Alexander Hamilton, who held the common masses in open contempt, and said of them, typically, "Your people, sir, is a great beast!"

The only thing linking that staid, sober, scholarly 1901 centennial edition of The Post with its present incarnation 80 years later is the name.

Which certainly matters not at all to Dunleavy. He's in the business of reaching a vastly different New York audience. The test of his effort, he believes, is readily apparent. The Post sells. As it says on each issue under its front-page masthead, The Post now is "America's fastest-growing newspaper." Its average daily sales are over 730,000, an increase of 240,000 since Murdoch bought the paper five years ago.

Why The Post grows while other competitors decline or die poses a journalistic puzzle. Not that newspaper size alone guarantees success. The New York Mirror, another tabloid, was selling more than a million copies a day when it folded years ago, and The Post still hasn't attracted sufficient advertising to assure it of a profitable future. At The News, its rival, you'll hear estimates that The Post losses caused by anemic advertising continue to run into the millions, a situation The Post maintains will be reversed as advertisers realize it's thriving and here to stay.

What Dunleavy will argue is that his paper simply understands its audience better, and reflects the reality of a metropolitan area like New York.

"When I first came here," he says, "there was no question The Post was a liberal paper. Now it isn't. There are very very few liberal readers left in New York. A lot of people are still socially liberal, but they're fiscally conservative. What you're reaching for is a very, very middle class guy."

He thinks the failure of The Daily News' afternoon paper, Tonight, proves the point.

They were Felkerized, he says, referring to Clay Felker, founder of New York Magazine with its highly personal literary style of journalism, and the person The News brought in to run Tonight. They tried to appeal both to a highly educated, wealthy audience as well as the subway strap-hanging masses, and failed to win either.

They tried to copy us, Dunleavy continued, without understanding what they were copying. He gestured toward copies of front pages of Tonight and The Post hung side by side on the wall.

"WOW!" read the massive type on one day of Tonight. "WOW!" shouted the identical head on that same day's Post. "MOMENT OF TRUTH" read another Tonight front page offering. "MOMENT OF TRUTH" cried The Post on the same newsstands.

There are many common threads running through these various experiences.

Easiest are the obvious ones: problems with unions; difficulties of physically getting papers to dealers in crowded city centers, that special bane of the afternoon editions; the inroads of TV viewing; changes in the educational and economic makeup of people who live in the great urban centers. And obviously afternoon papers in the major cities are having the hardest time.

Others are also easy to define. Competition, for one.

In Washington, Philadelphia and New York the struggling afternoon papers have faced sharp competition from good papers that are getting better. Ammerman of The Bulletin speaks with admiration of the job his opposite number, Eugene Roberts, has done editing The Philadelphia Inquirer, a morning paper whose editorial content improves steadily and holds a plethora of major awards to prove it.

The now-defunct Star in Washington had to deal with an ever-more aggressive and expanding Post unwilling to rest on its laurels from the Watergate era. Nor has The Times sat still in New York; in distinction of content and quality of design its special sections brilliantly appeal to readers the other papers need.

With all the "death in the afternoon" stories being written about some of the country's better-known afternoon dailies, an inevitable false impression is being created. Because some afternoon papers are in trouble or dying, doesn't mean all are doomed.

There are still four times as many afternoon daily papers published in America than morning ones. Some, solidly based in the prosperous and growing suburbs, are golden properties.

The success of Long Island's tabloid, Newsday, invariably cited by newspaper analysts, stands in sharp contrast to the problems of papers in adjoining New York City.

And Newsday by no means is unusual. The booming Record in Bergen County, N.J., offers another counterpoint of success to failure in the New York metropolitan area, and the same phenomenon can be found in other communities across the country.

Suburban afternoon papers are continuing to grow. In recent years small local papers, including some that were weeklies, have capitalized on the plight of the big afternoon dailies that increasingly were unable to deliver news late enough to match what people saw over TV.

They found they could offer something their local readers wanted, and have it up-to-date, too. Their product worked so well they switched to publishing daily evening papers and flourished.

Still, despite the success of many, and their greater total numbers, the trend continues against afternoon papers. More so-called "all-day" papers are being sold in major areas; they are, in reality, afternoon papers that come out earlier and earlier to catch the morning market.

The number of morning papers increases while the number of p.m.'s declines. Successful surviving p,m.'s are the only ones published in their areas. Even healthy afternoon papers outside the largest cities are reacting warily to the plight of others.

In Des Moines, Iowa, the afternoon Tribune has just cut back its circulation area, limiting it to the city's metropolitan area. It lopped off about 8,000 circulation spread through 22 of the state's 99 counties.

"The Tribune move was more of an offensive one than a defensive one," says Michael Gartner, editor and president of The Des Moines Register and Tribune Co. "We saw what was happening to afternoon papers and we decided we'd better move now to ensure that we didn't get caught in the trap. The Tribune is a good newspaper and a healthy one; I hope I'll be able to say the same 10 years from now."

But these afternoon-morning considerations mask a broader problem facing all papers. Nothing less than reading itself. Here, a paradox.

Latest Census Bureau data shows that illiteracy virtually has been eliminated in America. In a special report in its current issue, Presstime, trade journal of the American Newspaper Publishers Association, notes that only .5 percent of people 14 or older can be classified as illiterate. Yet, it adds, "We seem to be on the way to creating two cultures: one reading, one non-reading."

That non-reader group encompasses two kinds of people.

There are the "functional illiterates" capable of reading simple passages but not well enough to understand most newspaper sections. They number as many as 39 million people, or perhaps as high as 20 percent of the adult population. That figure, as the publication properly says, is "enormous, and only a few of them can read even the comics or sports sections."

And there are what the journal, admittedly in jargon, calls the "aliterates." That is, those who can, but won't, read. For the newspaper business, to say nothing of other forms of publishing, whether books or magazines, scholarly or sensational, they are the greatest worry.

One newspaper readership study concludes despairingly: "Reading was not a daily free-time activity for a majority of school-aged youths. They preferred watching TV, listening to the radio and talking to friends on the telephone."

After citing that depressing finding, Presstime adds:

"If 39 million citizens are functionally illiterate, and millions more can read but choose not to, newspaper people must be concerned for the future of their business."

All of which only intensifies the search for the proper formula to attract, and hold, newspaper readers.

The professionals are in agreement on something else. They distrust the readership surveys that purport to tell them what their readers want. Like Craig Ammerman, they prefer to trust in their own news instincts, and their own observations.

Dunleavy of The Post, for one, is scathing about surveys. He speaks scornfully of newspaper think tanks and talk of "upscale" and "downscale" readers, of luncheon discussions at "21" about the latest newspaper trends. "Demographics," he says. "What kind of a word is that? Readership surveys are a ripoff."

That's another way of saying part of the blame for the failure of The News' Tonight was too much reliance on consultants and not enough on common sense, a view that also finds supporters inside The News.

The News certainly has not been trying to offer excuses. In his widely quoted remarks announcing the end of Tonight, News publisher Robert Hunt said:

"We went all out to produce the liveliest, most interesting editorial package we could and, damn it, it didn't work. It was a bad marketing plan. We made a mistake and we're going to correct it."

And readership survey experts themselves are quick to turn around the complaints about them. "You cannot ask readers to become editors," says Ruth Clark, one of the best-known newspaper industry survey people. "That doesn't mean editors shouldn't delineate their market. They have to know who's out there."

Editors know that's only part of their challenge. As Ammerman and the rest in the beleaguered metropolitan centers will tell you, knowing who's out there doesn't mean they'll pick up your product instead of passing it by.