Splitting the atom some four decades ago was supposed to have released two nuclear genies from their bottles. The first - nuclear weapons - continues to alter the course of human history. But the second - the peaceful atom - has never performed its expected feats.
Now nuclear genie No. 2 is in danger of fading away altogether. The nuclear power industry, the most visible result of harnessing the atom, is in serious trouble. Although 72 plants are operating in the United States and 59 are officially under construction, no new plants have been ordered since December 1978. And questions of waste disposal and of safety, symbolized by the accident at Three Mile Island in 1979, continue to plague existing facilities.
Opponents and proponents of nuclear power agree that unexpectedly low demand for electricity - 2.1 percent lower in the first nine months of 1982 than the same period in 1981 - has discouraged construction of new nuclear plants. Peak demand for electricity last summer dropped for the first time since World War II. This has left utilities with the largest unused reserve capacity since 1938, according to the Department of Energy.
But economics is only one of three major factors weighing against new orders for nuclear plants, argues Eric E. Van Loon, executive director of the Union of Concerned Scientists in Cambridge, Mass., an antinuclear-power group. He says the huge current excess generating capacity, when added to safety questions and the sharp cost increases in building plants, ''combine to make no foreseeable scenario for any (nuclear plant) ordering in the next five years or so.'' Instead, utilities cancelled 18 nuclear plants in 1982.
As utilities plan later in this decade for plants to come on line in the 1990 s and beyond, he adds, it's ''reasonable to conclude that utilities will turn to renewables and other'' energy sources rather than nuclear power.
Not surprisingly, Manning Muntzing disagrees. The president of the American Nuclear Society (ANS) - a group of 13,000 scientists, engineers, and educators interested in the peaceful use of nuclear power - says an important role lies ahead for the friendly atom as a ''bridge'' to 21st Century renewable energy sources. He argues that abandoning nuclear power because of today's technical problems and low demand would be shortsighted.
But until those new energy sources are available sometime in the next century , he says, nuclear power must and will stay in the nation's energy picture. When the economy revives and energy demand begins growing at a rate of 3 or 4 percent a year, he points out, utilities will once again search for new generating capacity and will be reluctant to rely on any one energy source. ''For the rest of the century, it will be coal and uranium,'' he concludes.
Looking farther ahead, he envisions other roles for nuclear energy. ''There are no closed doors in peaceful nuclear uses,'' he says. Even though the time is still distant, ''If we're ever going to take E.T. home, we're going to have to send up compact nuclear reactors - along, perhaps, with solar panels - to power trips to remote destinations'' in space. In addition, agriculture, industry, and medicine will expand use of radioactive materials.
Mr. Muntzing says industry and government are addressing questions of reactor safety and waste disposal, both areas of public concern. ''There are hazards to any (energy) choices, the acid rain from coal plants, for example,'' he says. But as Americans look at the actual record of nuclear plants ''they will say the benefits outweigh the hazards. . . . They'll see that day in, day out, power is being produced and they're getting the benefits.''
Even the Three Mile Island accident, he says, had its bright side. ''TMI showed that when a problem occurs, we go out and get a solution to it. Since then we've seen more NRC (Nuclear Regulatory Commission) regulation, and more industry self-evaluation. No member of the public was affected. The utility has a great financial problem, but the public was protected.''
The nuclear waste problem, he says, is not technical - there is broad agreement in the scientific community that safe disposal is possible. Rather, he says, it's political. Recent legislation passed by Congress attempting to set a national policy on waste disposal is an encouraging step in the right direction, he says.
Muntzing, along with other nuclear-power advocates, points to the breeder reactor and fusion as future nuclear power sources that won't rely on exhaustible uranium for fuel. But the verdict is far from unanimous. Richard K. Lester, an associate professor of nuclear engineering at the Massachusetts Institute of Technology, says technical and economic factors make predicting the future roles of these technologies difficult.
Dr. Lester says that uranium will have to become much more scarce and expensive before the reduced fuel costs of a breeder reactor will outweigh its higher capital costs. In addition, other technologies could eclipse it.
''Work is under way here and in Japan to extract uranium from sea water,'' he says. ''If this proves to be economical, then the breeder would disappear entirely. Of course, this is impossible to say with certainty.''
The cloud hanging over fusion, he says, is whether machines can be built that are cost competitive with future alternatives, such as large-scale solar, when fusion technology becomes available ''several decades'' from now.
Nonetheless, when Dr. Lester recently delivered a paper entitled ''Is the Nuclear Industry Worth Saving?'' he answered ''yes'' to the question. ''The uncertainties of other options, particularly coal, and the uncertainty of demand suggest that it is prudent to not let the nuclear option disappear,'' he says.