TOKYO — Japan said Friday that it would seek to phase out nuclear power by 2040, a historic shift for a country that has long staked its future on nuclear energy but one that falls far short of the bold steps that the government had promised in the wake of the world’s second-largest nuclear power disaster last year.

Although the long-awaited energy policy was named the ‘‘Revolutionary Energy and Environment Strategy’’ by its authors, it extended the expected transition away from nuclear power by at least a decade, from 2030 to 2040, and includes caveats that appear to allow some plants to operate decades past the new deadline.

The government had been considering several options: whether to reduce the number of plants to zero over time or maintain enough reactors to provide a diminished but still substantial percentage of the country’s energy needs.

Before the nuclear accident at the Fukushima Daiichi plant, Japan depended on its reactors for about 30 percent of its electricity needs and had planned to raise that share to more than 50 percent by 2030.

The announcement comes after months of increasing anxiety and intense political pressure from those who believe Japan’s future is at stake.

Many political and business leaders argue that shuttering nuclear plants would doom the resource-poor country to high energy costs and a steeper economic decline than Japan is already facing. But many Japanese, while acknowledging the economic upheaval it could cause, have expressed hope that the country would phase out nuclear energy within two decades, and a nascent, but increasingly vocal, antinuclear movement has pressed for faster action.

While important for setting a tone, the announced strategy is subject to vast change, not only because of the long lead time, but also because the unpopular prime minister, Yoshihiko Noda, and his governing Democratic Party probably will lose the next national election, which could come as early as the next several months.

Analysts have suggested the Democrats timed the announcement to give them a political lift, but it is unlikely to appease the antinuclear movement or powerful business interests.

Those who favor a phaseout blasted the strategy Friday as too vague and drawn-out to bring real change.

‘‘It’s trickery with words and numbers,’’ said Tetsunari Iida, director of the Institute for Sustainable Energy Policies, a research group based in Tokyo. ‘‘The zero number might be symbolic politically, but in reality, it holds little meaning.’’

And the country’s most influential business federation this week made clear that phasing out nuclear power was ‘‘unrealistic and unreachable,’’ according to its chairman, Hiromasa Yonekura.

With the long-term energy plan set, the political battle is set to shift to the continuing struggle by the government to build consensus for reopening the vast majority of the country’s reactors, which were idled after the nuclear catastrophe amid public opposition to restarts until better safety regulations were in place.

The government has sought repeatedly to regain the public’s trust, most recently by scrapping its former nuclear regulator and appointing a new one. But the new regulator has already come under fire.

In announcing the energy plan, Motohisa Furukawa, the minister of state for national policy, said there was no change to the government’s quest to restart those reactors. And although the plan stipulates that no new reactors will be built, it leaves open the possibility than seven reactors that are in the works could be activated. That decision would be left up to the new nuclear regulator.