South Carolina Gov. Richard W. Riley warned yesterday that he would close the state's nuclear waste storage center to other states unless Congress adopts a proposal this year to establish regional sites by 1991.

Under a 1980 law, states already face a deadline next January to take care of their own low-level nuclear waste either by forming regional compacts with other states or by designating disposal sites within their own borders. But with that deadline barely six months away, Congress has not yet ratified any of the 10 regional compacts requested by 42 states or an independent plan by Texas.

The South Carolina Democrat told a House Energy and Commerce subcommittee that "if the matter is not resolved, I as governor will take every action legally possible to assure that the South Carolina site is limited to South Carolina's waste only."

South Carolina's Barnwell storage facility -- one of three sites across the country -- last year housed 47 percent of the nation's low-level radioactive waste. About one-fifth of the waste was generated in South Carolina.

Riley proposed what he termed a five-part compromise amendment to the 1980 law, which was enacted in large part because of his state's increasing uneasiness with its role as a dumping ground for nuclear waste.

The proposal, which has been introduced in the House by Arizona Democrat Morris K. Udall, would permit all states to continue to use the facilities at Barnwell, Hanford, Wash., and Beatty, Nev. In exchange, states would have six years to set up waste sites for themselves or their regions.

In the interim, the states would also have to curtail the volume of low-level radioactive waste, pay higher rates for the use of the existing sites, and meet a series of planning and construction deadlines or risk losing access to the three sites.

The proposal has sparked opposition from an unusual alliance of environmental groups and nuclear industries that say the deadlines are too strict and the volume limitations are either unworkable or safety hazards.

David Berick, testifying for the Environmental Policy Institute and the Sierra Club, said the proposal adopted unrealistic schedules for completing waste centers and "raises serious health and safety questions."

Edward M. Davis, president of the American Nuclear Energy Council, an umbrella organization for the nuclear industry, said it would be impossible to curtail low-level nuclear waste to the levels required by the proposal.