THE catch phrase of the 1970s, "Try it, you'll like it," is proving costly for those who tried nuclear power and didn't.Of the 13 nuclear power plants halted in the United States since 1963, none has completed the lengthy decontamination and dismantling process known formally as "decommissioning." Of these plants, officials at the four largest - Three-Mile Island in Middleton, Pa.; Fort St. Vrain in Colorado; Shoreham in Suffolk County, N.Y.; and Rancho Seco in 1989 - estimate the cost of the shutdowns will range from $200 million to $320 million and the process will take decades. The facilities are closing due to safety and cost concerns. "When you shut down a nuclear power reactor, you can't just turn off the lights and go home," notes Peter Erickson, senior project manager for the Nuclear Regulatory Commission (NRC). Besides monitoring the cooling of spent fuel in on-site water pools (there are still no temporary or permanent federal storage sites), most facility licensees elect to wait 30 to 50 years for the most radioactive elements in pipes, floors, and walls to decay. This reduces the danger of exposure to radiation for workers dismantling the plants. Only then will the physical plant be demolished or converted to other uses. For the shareholders of the Sacramento Municipal Utility District (SMUD), their Rancho Seco nuclear power plant here is the latest case-in-point. Twenty-five miles south of the state capital, Rancho Seco is the first major nuclear reactor to be closed by public referendum. Though power generation was stopped the day after a public vote in June 1989, the plant is still in the final phase of a preliminary closure process. Early next year, it will enter formal decommissioning. In 1963, a General Electric plant in Alameda, Calif., was the first reactor to be decommissioned. The shutdown process is still ongoing. No fuel is on site, but the physical plant is being monitored for levels of radioactivity in pipes, walls, and valves to allow a significant reduction in radiation levels before dismantling. The nuclear waste produced during 14 years of operation at Rancho Seco is enough to fill about 25 train boxcars. While it is kept cool in a water pool here, the Department of Energy (DOE) is considering a national repository for spent nuclear fuel at Yucca Mountain, Nev. Even if the decade-long study process there shows the site capable of isolating nuclear waste safely for the necessary 10,000 years, the site would not be ready until 2010. Meanwhile, the 200-plus maintenance, security, and emergency personnel on-site here will cost SMUD nearly $320 million by the plant's license expiration in 2008. For the short-term, federal nuclear-waste negotiator David Leroy is negotiating sites of temporary storage known as monitored retrievable sites in various states. "If such a temporary site is located and approved by 1998, our waste would go there," says SMUD's Jim Shetler. Marvin Mendonca, acting chief of the Decommissioning Section for the NRC, says each plant's design and operating history necessitate different review processes that are both painstaking and slow. All but two plants decommissioned before 1989 were in the 100-megawatt or less range; Rancho Seco, Three-Mile Island (closed in 1979), and Shoreham (closed in 1989) are in the 700-1,000 megawatt range. "The larger the plant, the bigger the possible problems," adds Mr. Erickson. Though each of the nation's 100 nuclear power plants are required to submit decommissioning plans five years before license-expiration dates, precipitous events precluded such foresight in many cases - most notably at Three-Mile Island, where electrical malfunctions caused a sudden meltdown. Shoreham, Rancho Seco, and Three-Mile Island "were closed prematurely without a ready plan," Mr. Mendonca says. "Each plan is unique to itself and has no precedent." Funding plans to insure the decommissioning will be completed are also reviewed in detail by the NRC. "We want to make sure no one else is stuck with the cleanup," says Mendonca. Funding is a minor incentive for spreading decommissioning over time, according to NRC's Bob Woods. Licencees hope improved, more cost-effective technology will be developed as time goes on, he says. Current national policy is for all spent nuclear fuel and its waste products to be stored in a single, permanent facility. In 1987, Congress mandated a study of Yucca Mountain. DOE recently began assessing fault lines and the traveling paths of groundwater at the site. Twenty-thousand tons of nuclear fuel now exist, according to Department of Energy spokeswoman Stephanie Hanna. Yucca Mountain will be capped at 70,000 tons, she adds. Rancho Seco accounted for half of the electric power under direct control of SMUD - a service area of about 1.5 million costumers - but had suffered repeated breakdowns over its 14-year life. Besides several steam generator leaks, a short-circuited light bulb in the control room stalled computers, allowing the plant to cool too fast. Rate increases due to burgeoning operating costs also were a major reason voters elected to close the plant. Though purchase contracts with four regional utility companies have filled the power void left by the shutdown, rate increases expected in 1995 and utility-contract expirations in 2000 have prompted recent moves for new power sources in Sacramento. SMUD general manager S. David Freeman last month submitted recommendations to his board for four local plants to be built over the next 10 to 15 years. He is recommending two projects in Canada, and smaller local wind, solar, geothermal, and hydroelectric facilities to fill the 916-megawatt gap left by Rancho Seco.