Nearly two years after the Chernobyl nuclear disaster, police have set up patrols to prevent residents from returning to the 18-mile evacuation zone around the atomic plant and to prevent vandalism in abandoned villages, the Soviet news agency Tass said Saturday.

At least 92,000 people were evacuated from 180 settlements in the danger zone following the April 26, 1986, accident at the plant's No. 4 reactor, the worst civilian nuclear disaster in history. Thirty-one people died in the incident.The disaster turned the Ukrainian countryside around the stricken plant, 75 miles north of Kiev, into a wasteland, but Tass quoted Kiev regional police chief Alexei Demchenyuk as saying that about 100 former residents have sneaked back into the zone.

Demchenyuk said police have not forced the evacuees to leave and have even helped them cut firewood and repair houses.

"We do not have a legal or moral right to force them to leave," he said.

The radiation level in the evacuated zone today remains "somewhat higher, as compared to ordinary radiation readings," Tass said.

But the health hazards and new housing built outside the zone for evacuees have not prevented some of the residents from trying to move back to the region.

"Some of the people who lived there prior to 1986 (still) try to return to their homes and farms by going around guard posts," Demchenyuk said. "These are mostly elderly people for whom it is difficult to settle in a new place. Our key task is to prevent the appearance in the health-hazardous zone of people not employed at the Chernobyl nuclear power station."

The No. 4 reactor that caused the disaster was permanently sealed in concrete. The other three reactors are in operation.

"It has been decided to set up a new system of militia patrols to maintain public order in Chernobyl," Demchenyuk said. "The patrols are assigned the task of keeping watch over the (18-mile) zone."

"The radiation level of these cultural treasures exceeds somewhat the permitted radiation standard," Demchenyuk said. "Therefore, the scientists and restorers were summoned to Chernobyl and now work on how to decontaminate and preserve them."

The town of Chernobyl, just south of the plant, had 12,000 residents before the evacuation. It dates to the 12th century.