After a 28-year lull, the United States seems ready to resume its flirtation with nuclear energy. Despite several high-profile incidents, including one that claimed two lives in 1999, Japan has never lost its interest in this power source. Europeans have gone back and forth on the issue: Green candidates have called on various governments to shut down their nuclear programs, but progress has been halting. Rising energy prices and California's woes have given the nuclear industry a fillip in recent months, and proponents of nuclear power have seized the initiative. Nuclear energy is a partial solution for what ails modern industrialized economies, but it raises important questions as well. They must be answered before the rush to build new nuclear plants resumes.

There has always been a strong case for nuclear energy. For a country like Japan, which has no energy supplies of its own, nuclear power was an indispensable part of national-security strategy: a means to safeguard independence. Proponents also claim that nuclear technology is more efficient than other energy sources, although close analysis shows that the numbers are not so solid. The alleged economies of nuclear power depend on accounting methods, and in particular how costs are distributed over time.

Nuclear power is more efficient if governments subsidize insurance costs, but that reasoning is circular when economic efficiency is the reason for building plants in the first place. In the U.S., in particular, where government subsidies are usually anathema -- there is little stomach for other forms of interference in the workings of the market -- the argument does not make sense.

In recent years, a key claim has been that nuclear power is a cleaner form of energy -- that as concerns about global warming mount, nuclear plants are the best way to cut greenhouse-gas emissions. Again, this argument sounds strange coming from Washington, where the government has been skeptical, at best, about the threat of global warming.

Moreover, nuclear power is environmentally friendly only if we overlook the other threats it poses. The most obvious danger is that of an accident. Unfortunately, we have had enough -- Three Mile Island and Chernobyl, to name the two most infamous -- to know that the danger is not just hypothetical.

Then there is the radiation that is created in every step of the production process, including the mining of uranium. Japan knows only too well that nuclear-power plants are not the only dangerous places. The two men who were killed in this country's worst nuclear-industry accident in Tokaimura in 1999 were working at a fuel-reprocessing facility.

Finally, there is the fuel and waste that is generated by nuclear-power plants. That radioactive material is hazardous to humans for hundreds of thousands of years, and no government has come up with ways to dispose of it safely. Nor are there adequate assurances that these materials can be safeguarded from individuals who might try to steal it to produce weapons or use it for nuclear blackmail. This "ultimate" environmental threat seems to balance the alleged benefits.

Nonetheless, governments appear certain to press ahead. The Japanese government last week approved the construction of two new nuclear-power stations. Chugoku Electric will start building a reactor in fiscal 2007 and a second plant three years later; each is planned to go into operation after five years. The two reactors, each with a capacity of 1.37 million kw, will be among the largest in the country.

The administration of U.S President George W. Bush has made a similar commitment. In a report released last week, a Cabinet-level task force headed by Vice President Richard Cheney endorsed an increase in nuclear-power generation. That is one part of a broad strategy that aims to increase U.S. production of oil, gas and coal. Another controversial element of the plan calls for oil and gas exploration in Alaska's Arctic National Wildlife Refuge.

There may well be good reasons to expand nuclear-power generation, but governments are not making a convincing case. In Japan, the policy has continued despite mounting public concern over safety. The public in the U.S. and Europe is also worried, and governments must respond to them if nuclear power is to have a future.

One option that deserves further exploration is conservation. In the U.S., in particular, there is an abiding belief in the right to consume gasoline at ridiculously low prices. Yet when encouraged to do so, consumers embrace conservation. A real debate on energy policy is long overdue. Governments around the world would be well-advised to hold one -- in earnest.