WASHINGTON - Regulators are investigating whether the radiation exposure was higher than originally estimated for workers who accidentally carried on their clothes tiny radioactive particles out of an Ohio nuclear power plant.

Estimates of exposure by the Nuclear Regulatory Commission differed from the assessment of the plant operator, the NRC said Tuesday.

Five workers left the Davis-Besse nuclear plant in February with the particles, which were found in hotel rooms and homes in at least three other states, according to FirstEnergy Corp., which operates the plant near Toledo.

The company had said that the particles, which are too small to see, didn't pose a health risk because they generated low level radioactivity.

Viktoria Mitlyng, an NRC spokeswoman, said urine and fecal samples indicate that the workers inhaled the particles, which means dose estimates could be much higher.

``We can't conclude what the internal exposure was until we take a look at exactly what particles were inhaled and how large those particles were,'' Mitlyng said.

While the situation is unusual, particles have been carried out of other plants before and the workers in question are healthy and still working, Mitlyng said.

Workers typically wear protective clothing in nuclear plants, then remove their suits in a safe area where they are screened to make sure radioactive particles do not escape. The NRC investigation earlier found that one of the three devices used to screen workers had been improperly set.