TOKYO — Efforts to stabilize the crippled nuclear power plant in Fukushima stalled Monday when engineers found that crucial machinery at one reactor required repair, a process that will take two to three days, government officials said.

A team of workers trying to repair another reactor, No. 3, was evacuated in the afternoon after gray smoke rose from it, said Tetsuro Fukuyama, the deputy chief cabinet secretary of the Japanese government. But no explosion was heard and the emission ended by 6 p.m., NHK, the national broadcaster, said.

Separately, NHK cited the Japanese Nuclear and Industrial Safety Agency as saying white smoke was coming from the building housing Reactor No. 2, where repairs to machinery were needed. Fukuyama said significantly higher radiation had not been detected around the two reactors.

On Tuesday morning, smoke or steam was reported to be rising from two of the reactors, but the company that owns the power plant, the Tokyo Electric Power Co., reported just after noon that no more smoke was being emitted.

By late Monday, electrical cables had been connected to all six of the reactor buildings, but much more work needed to be done. At the No. 3 and No. 4 reactors, damage from the earthquake and tsunami, as well as rubble from hydrogen explosions, was impeding the effort to restore operations.

An official at the U.S. Nuclear Regulatory Commission said Monday that Reactors No. 1 and No .2 were both too damaged for cooling systems to restart immediately, even when electricity was restored. But the official, William Borchardt, also said the situation at the plant appeared to be “on the verge of stabilizing.”

The NRC is advising the U.S. Embassy, supplying assistance to the Japanese and gathering information to benefit U.S. reactor safety.

The U.S. State Department, meanwhile, said it would offer potassium iodide to its staff members and dependents in the Tokyo region and to the north on Honshu, Japan’s main island and the site of the troubled power station, as a precaution against a possible radiation release.