By Kiyoshi Takenaka and Yoko Nishikawa
TOKYO (Reuters) - Exhausted engineers successfully attached a power cable to Japan's tsunami-crippled nuclear station on Saturday in a race to prevent deadly radiation from an accident now rated at least as bad as America's Three Mile Island in 1979.
Though it is still unknown whether that will be enough to restart water pumps needed to cool overheated nuclear fuel rods, it was at least a step forward at the six-reactor Fukushima plant in northeastern Japan, 240 km (150 miles) north of Tokyo.
Japan's unprecedented multiple crisis of earthquake, tsunami and radiation leak has unsettled world financial markets, prompted international reassessment of nuclear safety and given the Asian nation its toughest time since World War Two.
It has also stirred unhappy memories of Japan's past nuclear nightmare -- the U.S. atomic bombs dropped on Hiroshima and Nagasaki in 1945.
At Fukushima, nearly 300 engineers working inside a 20 km (12 miles) evacuation zone were focused on trying to restore power at pumps in four of the reactors.
"TEPCO has connected the external transmission line with the receiving point of the plant and confirmed that electricity can be supplied," the plant's operator Tokyo Electric Power Co said in a statement.
The next stage will be to check equipment is working and not damaged before trying to crank up the coolers at reactor No. 2, followed by 1, 3 and 4, it added.
If that works, it will be a turning point.
"If they can get those electric pumps on and they can start pushing that water successfully up the core, quite slowly so you don't cause any brittle failure, they should be able to get it under control in the next couple of days," said Laurence Williams, of Britain's University of Central Lancashire.
If not, there is an option of last resort under consideration to bury the sprawling 40-year-old plant in sand and concrete to prevent a catastrophic radiation release.
That method was used to seal huge leakages from the 1986 Chernobyl disaster.
Japan has raised the severity rating of the nuclear crisis from level 4 to level 5 on the seven-level INES international scale, putting it on a par with the Three Mile Island accident in 1979, although some experts say it is more serious.
Chernobyl, in Ukraine, was a 7 on that scale.
The operation to avert a large-scale radiation leak has overshadowed the humanitarian aftermath of the 9.0-magnitude earthquake and 10-meter (33-foot) tsunami that struck on March 11.
Nearly 7,000 people have been confirmed killed in the double natural disaster, which turned whole towns into waterlogged and debris-shrouded wastelands.
Another 10,700 people are missing with many feared dead.
Some 390,000 people, including many among Japan's aging population, are homeless and battling near-freezing temperatures in shelters in northeastern coastal areas.
Food, water, medicine and heating fuel are in short supply.
"Everything is gone, including money," said Tsukasa Sato, a 74-year-old barber with a heart condition, as he warmed his hands in front of a stove at a shelter for the homeless.
Health officials and the U.N. atomic watchdog have said radiation levels in the capital Tokyo were not harmful. But the city has seen an exodus of tourists, expatriates and many Japanese, who fear a blast of radioactive material.
"I'm leaving because my parents are terrified. I personally think this will turn out to be the biggest paper tiger the world has ever seen," said Luke Ridley, 23, from London as he sat at Narita international airport using his laptop.
"I'll probably come back in about a month."
Amid their distress, Japanese were proud of the 279 nuclear plant workers toiling in the wreckage, wearing masks, goggles and protective suits sealed by duct tape.
"My eyes well with tears at the thought of the work they are doing," Kazuya Aoki, a safety official at Japan's Nuclear and Industrial Safety Agency, told Reuters.
G7 INTERVENTION FOR YEN
The Group of Seven rich nations, attempting to calm global financial markets after a tumultuous week, agreed on Friday to join in a rare concerted intervention to restrain a soaring yen.
The U.S. dollar surged more than two yen to 81.80 after the G7's pledge to intervene, leaving behind a record low of 76.25 hit on Thursday.
Japan's Nikkei share index ended up 2.7 percent, recouping some of the week's stinging losses. It has lost 10.2 percent this week, wiping $350 billion off market capitalization.
The plight of the homeless worsened following a cold snap that brought heavy snow to worst-affected areas.
Nearly 290,000 households in the north were still without electricity, officials said, and the government said about 940,000 households lacked running water.
Aid groups say most victims are getting help, but there are pockets of acute suffering.
"We've seen children suffering with the cold, and lacking really basic items like food and clean water," Stephen McDonald of Save the Children said in a statement on Friday.
(Additional reporting by Linda Sieg, Nathan Layne, Elaine Lies, Leika Kihara, Jon Herskovitz, Joseph Radford and Chris Gallagher in Japan; Fiona Ortiz in Madrid; Writing by Andrew Cawthorne; Editing by Robert Birsel)