FUKUSHIMA, Japan - (AP) - Officials are racing to restoreelectricity to Japan's leaking nuclear plant, but getting the powerflowing will hardly be the end of their battle: With its mangledmachinery and partly melted reactor cores, bringing the complexunder control is a monstrous job.

Restoring the power to all six units at the tsunami-damagedcomplex is key, because it will, in theory, drive the maze ofmotors, valves and switches that help deliver cooling water to theoverheated reactor cores and spent fuel pools that are leakingradiation.

Ideally, officials believe it should only take a day to get theFukushima Dai-ichi nuclear under control once the cooling systemsare up and running. But it could take days or weeks to get thosesystems working.

"We have experienced a very huge disaster that has caused verylarge damage at a nuclear power generation plant on a scale that wehad not expected," Hidehiko Nishiyama, deputy director general ofJapan's Nuclear and Industrial Safety Agency, told reporters lateMonday.

The nuclear plant's cooling systems were wrecked by the massiveearthquake and tsunami that devastated northeastern Japan on March11. Since then, conditions at the plant have been volatile; plumesof smoke rose from two reactor units Monday, prompting workers toevacuate units 1-4.

The crews resumed the work early Tuesday, plant spokesmanMotoyasu Tamaki said.

In another setback, the plant's operator said Monday it had justdiscovered that some of the cooling system's key pumps at thecomplex's troubled Unit 2 are no longer functional - meaningreplacements have to be brought in. Tokyo Electric Power Co. saidit placed emergency orders for new pumps, but it was unclear howlong it would take for them to arrive.

If officials can get the power turned on, get the replacementpumps working and get enough seawater into the reactors and spentfuel pools, it would only take a day to bring the temperatures backto a safe, cooling stage, said Ryohei Shiomi, an official with theNuclear and Industrial Safety Agency.

And if not?

"There is nothing else we can do but keep doing what we've beendoing," Shiomi said.

In other words, officials would continue dousing the plant inseawater - and hope for the best.

An official of the U.S. Nuclear Regulatory Commission said inWashington that Units 1, 2 and 3 have all seen damage to theirreactor cores, but that containment is intact. The assessmentdispels some concerns about Unit 2, where an explosion damaged apressure-reducing chamber around the bottom of the reactor core.

"I would say optimistically that things appear to be on theverge of stabilizing," said Bill Borchardt, the commission'sexecutive director for operations.

What caused the smoke to billow first from Unit 3 and then fromUnit 2 on Monday was under investigation, nuclear safety agencyofficials said. In the days since the earthquake and tsunami, bothunits have overheated and seen explosions outside their reactorcores.

Workers were evacuated from the area to buildings nearby, thoughradiation levels remained steady, the officials said. It was asetback in efforts to rewire the plant, where officials had hopedto finish connecting all six reactor units to the grid on Tuesday.

The World Bank said Monday that Japan may need five years torebuild from the disasters, which caused up to $235 billion indamage, saying the cost to private insurers will be up to $33billion and that the government will spend $12 billion onreconstruction in the current national budget and much more later.

All told, police estimate around 18,400 people died from the9.0-magnitude quake and tsunami. More than 15,000 deaths are likelyin Miyagi, the prefecture that took the full impact of the wave,said a police spokesman.

Police in other affected prefectures declined to provideestimates, but confirmed about 3,400 deaths. Nationwide, officialfigures show the disasters killed more than 8,900 people and leftmore than 12,600 missing, but those two lists may have someoverlap.

The disasters have displaced another 452,000, who are inshelters.

Links and information for relief efforts