Confronted with worse-than-expected damage at its battered nuclear plant, Tokyo Electric Power Co. on Tuesday revised its strategy for cooling Fukushima Daiichi’s reactors. However, the utility company reaffirmed its goal of stabilizing the facility — and ending the country’s nuclear crisis — within six to nine months.

Tepco was forced to overhaul its road map after learning last week of a substantial meltdown in the unit 1 reactor at the Fukushima Daiichi plant, on Japan’s northeastern coast. Fuel pellets had collected at the bottom of the pressure vessel, burning small holes or cracks in the containment vessel that allowed coolant to leak out. Japanese authorities say they fear similar scenarios have occurred at units 2 and 3, though engineers have not entered those reactor buildings.

Rather than flood the reactors with fresh water — a strategy outlined in the initial road map, released April 17 — Tepco plans to build a circulation system. Water will be pumped into the pressure vessel, decontaminated after it leaks out, then pumped back in.

Although Tepco still says it will be able to shut down the three troubled reactors by January or thereabouts, it faces increasing skepticism from the government and the Japanese people, who complain that Tepco has too often misjudged the severity of the situation.

Damage at the unit 1 building became clear only last week, when engineers fixed a gauge that measures water levels. Tepco had said for weeks that the fuel rods in unit 1 were 60 percent covered with water. It turned out that the fuel rods in the vessel were fully exposed.

Amid the worst nuclear emergency in a quarter-century, 80,000 people who lived within 12 miles of the plant have fled their homes. And Japan’s government has reevaluated its energy policy, calling for the shutdown of one earthquake-prone nuclear plant southwest of Tokyo.

Separately, Japan’s government agreed Tuesday to allow investigators from the International Atomic Energy Agency to visit and assess the Fukushima Daiichi plant from Tuesday to June 2.

“The acceptance of this investigative team will be very useful in sharing Japan’s experiences with various countries around the world,” Chief Cabinet Secretary Yukio Edano said.

Tepco’s revised road map includes several broader new goals, including plans to boost tsunami preparedness and improve conditions for workers.

Even as authorities try to restore the cooling system for the crippled reactors, they face numerous challenges. Much of the pumped-in coolant has been leaking, leaving pools of contaminated water that could take years to clean up. A series of explosions days after the March 11 earthquake and tsunami turned the facility into a field of radioactive debris. Nuclear experts have said that it will take decades to fully decontaminate the area around the plant.