After nearly three decades' courting of the nuclear industry, South Carolina reversed that posture today and informed the Nuclear Regulatory Commission that it will refuse to accept any nuclear wastes from the Three Mile island accident or from other reactor shutdowns related to it.

In a letter released today, South Carolina Gov. Richard W. Riley told NRC Chairman Joseph M. Hendrie that "our waste management program cannot accommodate the excess wastes from TMI or from any of the unscheduled reactor shutdowns."

Riley said he was referring to "potential" shutdowns of reactors in other parts of the country that might be ordered to assess and mofify reactor systems based on the TMI experience.

The governor's decision apparently means that radioactive waste from the Pennsylvania accident and from related reactor shutdowns will have to be shipped cross-country for burial in Washington, Idaho or Nevada. Two truckloads of low-level waste from Three Mile Island that, were turned back by South Carolina health officials last week because of fears that some high-level waste was mixed in were sent Wednesday to a Department of Energy-operated burial site near Richmond, Wash.

South Carolina's site in the town of Barnwell, which has been operating since 1971, is licensed to bury only low-level nuclear waste. It is the only such site east of the Rockies, and contains an estimated 90 percent of the nation's low-level nuclear trash.

Riley, who campaigned for governor last year promising that he would not allow South Carolina to become the nation's "nuclear dumping ground," said he would reject the Three Mile Island waste because "what was intended to be a regional facility to handle the low-level waste for the south-eastern and southern regions of the country has, in fact, become a national facility for virtually all the low-level commercial waste east of the Rocky Mountains."

Aides said Riley is concerned that if the 250-acre site at Barnwell fills up too quickly, South Carolina taxpayers will have to foot the bill sooner than expected for "perpetual maintence" once its operator, Chem-Nuclear, pulls out.

Riley said that even without the Three Mile Island waste, he anticipates that the total annual volume limit (200,000 cubic feet per month) placed on the Barnwell site by state health officials will be met or exceeded.

Riley urged Hendrie and the federal government ot formulate a "national low-level waste management plan based on a regional network of low-level burial sites." As in the case of "high-level commercial waste," Riley wrote, "this is a national problem which requires a national solution."

Riley is the first top official in the state for nearly 30 years to publicity voice skepticism about the extent of the nuclear industry in South Carolina. Since the early 1950s, state officials have wooed the industry vigorously, saying that nuclear power created jobs for thousands of South Carolinians.

South Carolina has the largest concentration of nuclear facilities in the nation. Riley announced recently that the state needs to "pause and see where we're headed" regarding nuclear power. He said he will oppose any future nuclear reactors in South Carolina, although he will not interfere with any in operation or on the drawing broads.

South Carolina generates more than 45 percent of its electricity from nuclear power.