TOKYO (AP) _ On a former U.S. Air Force base on the outskirts of Tokyo sits a back-up capital for Japan, a ghost town of bunker-like concrete buildings.

The rooms are sparsely furnished with metal tables and chairs, the basements filled with tons of canned food and a kerosene generator large enough to power a small town. There is even a well for water.

At the center of it all is a fully equipped crisis command center, with desks facing large wall-mounted viewing screens. There is a tall black leather chair reserved for the prime minister.

Following the catastrophic earthquake that flattened much of Kobe four years ago, Japanese officials have scrambled to prepare for what scientists say is the inevitable: a similar or even stronger quake hitting Tokyo.

But while they have tried to apply the lessons learned from Kobe, where bureaucratic paralysis was blamed for needlessly inflating the death toll of 6,425, experts stress a large quake in Tokyo could pose a host of new problems.

``There are a lot of things Kobe didn't prepare us for,'' said Hiroatsu Fukuda, a researcher at Tokyo's Waseda University. ``Tokyo really isn't ready.''

With a population of 12 million, nine times that of Kobe, Tokyo is a disaster waiting to happen.

The city sits on one of the most earthquake-prone spots in the world. Nearly 20 miles beneath its streets, three gigantic slabs of the Earth's crust creep in different directions at rates of barely an inch a year.

Sometimes these tectonic plates snag on each other, causing tension to build until they snap forward again.

An estimated 10,000 Tokyo residents died in 1855, the last time a major earthquake struck directly below the city _ a type of tremor called ``chokkagata'' in Japanese.

And that quake was not even the magnitude of the feared ``Big One.'' Seismologists expect a magnitude-8 shock to hit somewhere along the coast west of Tokyo with the force of a 50-megaton atomic bomb. The last time that happened was in 1923, and as many as 150,000 people died.

While a quake of that size remains a constant danger, experts say a smaller _ but still deadly _ jolt from directly below the city will probably hit first. A series of moderate shocks, most too deep to be felt by residents, and forecasts based on historical earthquake cycles indicate Tokyo could be due.

``A chokkagata is said to be imminent,'' said Toshio Nara of the Tokyo city government's disaster planning division.

City officials predict a 7.2-magnitude earthquake of that type, similar to the one that struck Kobe, would kill more than 7,000 people, injure 160,000 and leave at least 2.3 million homeless.

More than a half-million buildings would burn or collapse, inflicting damage worth several times Kobe's $120 billion. World financial markets could also panic as trading in Tokyo crashed to a halt.

Even so, officials say they are far better prepared than they were four years ago before the Kobe quake.

At that time, then Prime Minister Tomiichi Murayama waited for the bureaucracy to take the lead in responding. But the bureaucrats refused to budge until local governments applied for help through regular channels _ slowing relief by hours and even days.

New laws give the prime minister clear powers to order the military and emergency services into action. To further speed response, a state-of-the-art computer system has been developed that gives instant damage estimates and the locations of rescue services.

``Lack of information was a real problem at Kobe,'' said Mamoru Nakajima of the national government's Earthquake Disaster Planning Division.

Another was water and toilets. Survivors had far more difficulty finding them than other essentials, like food. Since Kobe, Tokyo has tripled its number of portable toilets and increased the amount of drinking water stored in cisterns beneath public parks to a 4 1/2-day supply.

But problems remain with the government's readiness, experts say.

One is a failure to adequately plan for the presence of 3.7 million commuters who pour into Tokyo by trains every weekday.

Commuters weren't a problem in Kobe because the earthquake hit at dawn, before the morning rush. But a daytime quake could leave Tokyo aid stations overwhelmed by up to 10 times the expected number of refugees.

Worse, city plans for resupplying those stations assume that citizens will obey orders to stay off major roads. ``That's nonsense,'' said Waseda University's Fukuda, who predicts millions of refugees will clog Tokyo's streets.

Then there are the hazards that can't be predicted.

Panic, for example, could increase casualties if it seizes crowds trapped in buildings or subways.

``The unexpected can ruin the best-laid plans,'' said Nara, the city disaster planner.

Still, Koji Arai, caretaker at the back-up capital complex, said the crisis center is ready to take over should all else fail.

``If downtown gets it, we'll be OK,'' he said.