The chimes that sound from Hiroshima's Peace Memorial Park each morning at 8:15 are hard to hear nowadays unless you are very close to them.

A few blocks from the park, the chimes that mark the precise time the atomic bomb exploded over this unsuspecting city in 1945 -- passing the world from one age to another -- are lost in the din of streetcars, whistles and crowds. A modern industrial city of more than a million people is gearing up for a new day.

The things that modern Hiroshima stands for as it prepares for Aug. 6, 1985, the 40th anniversary of the day the clocks stopped, are an odd mixture of material wealth and spiritual leadership in the global campaign against nuclear weapons.

The pleasure boats moored along Peace Park are proof of success in the first pursuit. But people here worry that the fight for disarmament is faltering; that as time moves forward, the world is forgetting the horrors of nuclear weapons and will use them again.

"The atomic bomb is always there in the back of my mind," said 18-year-old Terukazu Ooshige, a high school student. It is, understandably, a common remark in a city where only a small number of people are professional activists but everyone cares.

It was a clear Monday morning when the B29 bomber "Enola Gay" appeared high over Hiroshima, which stands on a series of islands in the Ota River estuary. The plane was carrying a 10-foot-long uranium bomb code-named "Little Boy" that would explode with the power of 20,000 tons of TNT.

At the time, the United States was preparing for an invasion of the Japanese mainland that, in some estimates, would have cost 1 to 2 million casualties on both sides. It was hoped in Washington that this bomb and others would force a decision to surrender and end the need for the invasion.

The bomb descended by parachute, and, as schoolchildren here can explain, was detonated 1,900 feet above the city center for maximum destructive effect. The heat -- for an instant as high as 300,000 degrees centigrade -- blistered roof tiles, melted glass and stripped the skin from human backs. The blast ruptured intestines, buckled concrete bridges and flattened houses on top of their owners.

The bomb killed close to 100,000 people on the spot and incinerated five square miles of homes and workplaces. Windows as far as 10 miles away were blown in. The mushroom cloud rose seven miles into the sky.

Three days later, a second bomb obliterated Nagasaki, another coastal city 175 miles to the southwest. Six days after that, Japan surrendered.

The agony was just beginning, however. In ensuing years, many people who survived the blasts began suffering from a horrible collection of radiation-linked diseases -- leukemia, breast cancer, tumors and general fatigue. Tens of thousands more died, and bomb-related deaths continue today.

"Are you still alive? For many years, that was our hello," recalls Satoru Kitagawa, a retired government employe who suffered only bruises in the blast but spent years going from doctor to doctor with ailments he believes were caused by radiation.

In view of this past, visitors to Hiroshima are often surprised to find so few physical signs of the destruction. Only one ruin remains, the commercial exhibit hall whose rusting dome has become a symbol of the city. Office buildings crowd in on Peace Park. Indeed, Hiroshima is indistinguishable in almost every other way from a dozen other medium-sized cities in Japan.

Economic life revolves around the Mazda Motor Corp., the largest employer. Two huge plants on the riverfront employ about 28,000 people and turn out close to a million vehicles per year. Other local factories produce industrial machinery, furniture and electronics products.

Life after hours revolves around the Hiroshima Carp, the professional baseball team that swept the Japan Series, the equivalent here of the World Series, in 1984 and is going strong this year. Their home stadium is a stone's throw from Ground Zero. They probably have done more than anyone to diversify Hiroshima's image.

People in Hiroshima have the same mundane concerns about urban existence as city dwellers everywhere. Mobsters known as yakuza are said to be growing strong and putting the squeeze on construction firms. The city and national governments are squabbling over facilities vacated when part of a university moved elsewhere. The city airport is too small.

What sets Hiroshima apart, of course, is its past and people. Today, it is home to 114,000 of the 367,000 people in Japan who are officially registered as hibakusha, literally "explosion-affected people." They range from retired laborers to company chairmen and form a special class in the local society. About 8 percent of the city's annual $1.4 billion budget goes for aid and free medical care for them.

Some live in seclusion and refuse to talk of their experiences. Others, like Kitagawa, have conquered the anxiety that gripped them for years and today seem to draw emotional sustenance from recounting that day for visitors.

On a national scale, the bomb has come to symbolize Japan's suffering in general during the war. Indeed, in some minds, it has dimmed recollection of Japan's role in instigating the war, first with attacks in China and then the bombing of Pearl Harbor. In this view, Japan emerged fom the war as victim, not aggressor.

In his famous radio address of Aug. 15, 1945, announcing the surrender, Emperor Hirohito referred to a "new and most cruel bomb." With that, and subsequent claims by the occupation authorities, millions of Japanese accepted the American orthodoxy that the bomb shortened the war.

But in view of the hideous effects on the people of Hiroshima and Nagasaki, the Japanese people stop short of saying it was a good thing.

In recent years, some academics have taken exception to the war-shortening theory. It is argued that what most hastened the surrender was the Soviet Union's entry into the Pacific war on Aug. 9.

In the preceding weeks, Japan had been trying desperately to get the Soviets, until that time neutral toward Japan, to persuade the Americans to negotiate for peace. The Soviets, it was believed by some in 1945, would want an independent Japan to be preserved to serve as a buffer against the Americans in the Pacific. Soviet entry into the war, however, could increase the threat to Japanese territory.

There are also suggestions, in some cases from bomb survivors, that the bomb was dropped so that the Americans could test it on a real city while there was still time, or that the bomb was intended as a demonstration to intimidate or warn the Soviet Union, which the United States already knew would emerge as its prime rival in the postwar world.

But Hiroshima's official message to the world today is that the tragedy occurred because of war. Who dropped the bomb on today's "Peace City" is held to be not important.

Since 1947, when hundreds of shanties were torn down to make way for Peace Park near Ground Zero, successive city administrations have devoted enormous time, money and personnel to a worldwide campaign. Mayor Takeshi Araki has addressed the U.N. General Assembly and this year sent letters to President Reagan and Soviet leader Mikhail Gorbachev appealing for disarmament.

In the park, the city maintains a powerful Peace Memorial Museum, where visitors silently gaze on such relics as melted bottles, tattered school uniforms and the front steps of the local Sumitomo Bank branch, which bear the shadow of an unknown person who was sitting on them when the nuclear flash seared the city.

"Our goal is to convey accurately the reality of Hiroshima to the next generation," said Yoshitaka Kawamoto, a bomb survivor who is director of the museum. "The day is coming when there will be no one who can talk of it from experience. But I think the twisted bottles and bones will tell the story."

Hiroshima children begin learning about the bomb in elementary school.

They select research topics -- what a bomb would do to today's Hiroshima, for instance -- work on them in groups and then present their findings to the class.

Business organizations take part, too. The local Junior Chamber of Commerce has commissioned a Hiroshima Symphony to be premiered at this year's national Jaycees' convention, which will be held here in the fall.

Even without formal indoctrination, however, people here cannot escape the bomb. The local media carry almost daily news of actions by survivor groups. Everyone seems to have an aunt who died or a neighbor who survived. And the peace dome and park are constant reminders.

About 1.5 million people visit the park and museum every year. Schoolchildren arrive from around Japan -- on some days as many as 10,000. They cluster around the park's memorials to the dead, take turns ringing a mammoth "peace bell" and deposit pleas for peace on wooden plaques at the dome.

Each summer, as another anniversary approaches, tablets that list the victims are taken from storage, and the names of those who succumbed during the past year are added. Aug. 6 culminates with a series of emotional ceremonies, sharing the theme "Never Again!"

Still, many people in Hiroshima worry that the campaign is losing steam. Despite their efforts, in much of Japan, people think of the atomic bombs only twice a year, when they see television news reports on anniversary events here and in Nagasaki.

Activists here hate to admit it, but the antinuclear movement in Western Europe seems more effective than their own. The campaign here at the national level has been hamstrung for years by ideological feuding between groups allied with Japan's Communist and Socialist parties.

U.S. warships, it is believed here, routinely violate official Japanese strictures against carrying nuclear weapons into Japanese ports. Newspapers dutifully log the ships' arrivals, but there is now rarely a concerted effort to stop them.

Residents such as Toru Okada, 50, prefer to talk of Hiroshima's future. As an executive at the city's main brokerage house, Utsumiya Securities Co., he is excited about the internationalization of the economy here and around Japan. He notes with satisfaction that basketballs used in the Los Angeles Olympics were made in his city.

The city's stock exchange is one of seven regional markets in Japan. For years after the war, it closed for Aug. 6. But later, pragmatic businessmen -- perhaps reflective of the entrepreneurial drive that has attracted a new image for Japan if not entirely for Hiroshima -- decided to change.

"If you're going to do business," said Okada, "it makes no sense to close down when everyone else is open."