In the now-abandoned town of Futuba, inside the 12-mile evacuation zone around the Fukushima Daiichi plant, a sign that arches over the entrance to a main street reads: “Nuclear power is the energy of a bright tomorrow.”

But today, as workers continue their struggle to contain radioactive leakage at the plant, resource-poor Japan has been forced to scale back that commitment to nuclear power and is scrambling to find alternatives. A new energy policy, which Japanese Prime Minister Naoto Kan began to outline this week, would emphasize solar and wind power and require pricey investment and yet-to-be-determined innovation.

In a speech this week, Kan mentioned several precise targets. By 2020, he said, solar power should cost one-third of what it does now. By 2030, it should be down to one-sixth. And in a decade or so, Japan should be receiving 20 percent of its total energy supply from renewable sources, more than doubling the current share. Kan also said that, by 2030, about 10 million buildings should have solar panels.

Kan is urging his country to use less energy. And he said he wants Japan’s nuclear program to be safer and smaller. All of these steps, he knows, will require drastic change. As he outlined the basics of Japan’s new energy policy, Kan used the word “challenge” seven times.

Before the Fukushima accident — the world’s most severe nuclear crisis in a quarter-century — Japan had spent decades cheerleading for atomic power. Nuclear plants provided 30 percent of the country’s energy, with plans for 50 percent reliance by 2030.

The Fukushima accident, triggered by Japan’s March 11 earthquake and tsunami, has prompted large-scale anti-nuclear demonstrations and a nationwide debate about plant safety. But government officials insist that the country isn’t dropping nuclear power entirely, and there are plenty of reasons for that stance. Nuclear power reduces Japan’s fossil fuel imports. It emits no carbon dioxide. And it’s cheap.

But its place in Japan’s energy future has clearly shifted. Japan is unlikely to build new reactors, Kan said this week in an interview with the Financial Times, another unmistakable sign that the country has turned away from its pre-March 11 nuclear energy targets.

Only 17 of Japan’s 54 reactors are currently generating power, with 22 shut down for planned or unplanned inspections, according to the World Nuclear Association. In addition, two reactors at a quake-prone plant southwest of Tokyo were halted at the government’s request. Nine stopped automatically on the day of the earthquake, as designed, and have remained offline. And the four stricken reactors at Fukushima Daiichi will never again be used for power generation.

Because of the Fukushima crisis, Tokyo Electric Power Co. — which accounts for 27 percent of the nation’s power — has been left with major shortages. To reduce usage and avoid blackouts during the peak summer months, the government has called for a 15 percent cut in energy use beginning July 1. But already in Tokyo, escalators at subway stations don’t run. Department stores keep their lights dimmed. Businesses don’t run their air conditioners full-blast.

Kan wants some of these changes to be long-term, calling for “a new culture of energy consumption.”

Although the prime minister has set new energy targets, he has yet to give specifics of how those goals will be reached — particularly how Japan will drastically reduce the price of solar energy. According to Japan’s Ministry of Economy, Trade and Industry, solar power has a generation cost of 60 cents per kilowatt-hour, while nuclear power costs 6 to 8 cents per kilowatt-hour. If Japan is to reach its target price reduction, solar power by 2030 will cost roughly 10 cents per kilowatt-hour.

Proposed legislation would oblige utility companies to buy electricity from mega-solar projects. But Japan is also hoping that technology advances can reduce the cost. Within the government, concerns about renewable energy go beyond price: The economy ministry, in a 2010 report, mentioned that some renewable energy sources are “unstable, and facilities can be established only in a limited number of areas due to the required conditions of topography and so forth.”

“I think it’s good to set an ambitious renewable energy vision,” said Ken Koyama, director of the Tokyo-based Institute of Energy Economics. But counting on solar power without first figuring out how to lower the price “will be risky,” he said, and pulling it off will be difficult. If all of central Tokyo were blanketed with solar panels, it would supply as much energy as one nuclear reactor, Koyama said.

But with its supply of renewable energy as yet undeveloped, Japan is turning in the interim to fossil fuels. The Institute of Energy Economics estimates that Japan this year will need to import an extra 110,000 to 140,000 barrels of oil per day, an increase of 3 to 4 percent from the usual amount. A parallel increase of about 10 percent is forecast for imports of liquefied natural gas.

Special correspondent Akiko Yamamoto contributed to this report.