Nuclear power experts estimated yesterday that it could cost up to $430 million and take four years for the Three Mile Island atomic plant to recover from the March 28 accident in Pennsylvania that put it out of operation.

A study by the Bechtel Power Corp., for Three Mile Island owner General Public Utilities Corp., said the plant can be safely recommissioned. After the spring accident, when the reactor overheated and a meltdown was feared, the possibility was raised that the plant would never reopen.

Also at that time it was estimated that the plant could be returned to operation at a cost of $140 million to $280 million and a delay of tow to three years.

Beectel's study estimates that the rehabilitation of Three Mile Island Unit 2 could cost $450 million, including up to $85 million to replace the damaged reactor core.

GPU added $25 million to the Bechtel estimate to cover "possible cost uncertainties."

Bechtel projected the plant could be restarted in June 1983.

"Bechtel also estimated that the time schedue could vary six months either way," GPU said. "The timetable does not consider extraordinary legal, political or regulatory delays which could add to the cost estimate," GPU said.

GPU's total estimate of $430 million could change because the extent of the plant contamination is as yet unknown, and there is the possibility modifications that could come out of reviews of the accident by the Nuclear Regulatory Commission and the presidential blue-ribbon commission.

But the $430 million figure represents what is believed to be the first best guess of the cleanup cost after the nation's worst commercial nuclear accident.

GPU said that, "Some of the expenditures involved in returning the unit to service are expected to constitute plant improvement and can be capitalized and recovered over the life of the facility."

That means the utilities that own Three Mile Island will be able to pass some of the rehabilitation cost to consumers in the form of a rate hike, GPU spokesman Jack Dunn said.

Workers still have been unable to enter the plant's containment building, which holds radioactive water from the accident. The Bechtel report said the GPU executives hope to gain entrance to the containment struture later this year or early next year.

GPU Chairman William H. Kuhns said that "safety of the operation will be paramount. Strict safeguards will be established to contain the radiation and insure both public and worker safety."

After entry and decontamination of Unit 2, GPU said, waste water would be removed by remote control. It would be stored temporarily on the site and later transported "to a permanent disposale site. No radioactive water would be stored permanently at the facility."

According to GPU, "The Bechtel report indicates that so far there has been no evidence uncovered which would indicate that the unit cannot be safely decontaminated and restored to service."

Yesterday, almost four months after the March 28 accident, 15 reporters were taken on the first tour of the plant conducted specifically for the news media.