The accident on Three Mile Island underlines the dangers of nuclear power, but it may be diverting attention from a more fundamental issue: the economics of nuclear power. The great appeal of nuclear power over coal, oil and solar energy in its many forms has always been economic. Its early proponents talked of energy "too cheap to meter."

It has been some time now since we've heard the "electricity too cheap to meter" refrain. As early as 1975, Donald Cook, chairman of the board of American Electric Power, the largest U.S. utility, was saying that "an erroneous conception of the economics of nuclear power" had sent U.S. utilities "down the wrong road." Cook was not alone in reading the economic handwritting on the wall. Reactor orders from U.S. utilities had come to a virtual halt by 1975.

The cost of electricity is determined in part by the initial construction costs of the generating plant. For nuclear plants these costs are soaring. Secretary of Energy James Schlesinger proposes to attack these escalating costs by reducing the 10 to 12 years that now elapse between the application for the first permit and the plant's coming on stream. But after Three Mile Island, that process is likely to be slowed down rather than speeded up.

Safety and economics cannot, of course, be entirely separated. The accident at Three Mile Island is certain to lead to greater expenditures to ensure the safety of nuclear plants. These additional costs may be the financial straw that breaks the nuclear camel's back.

Even before the runaway reactor at Three Mile Island had cooled, the New York State Power Authority announced it was abandoning a proposed 1,200-megawatt nuclear power plant on which it had already spent $147 million on design alone. The estimated construction cost had climbed from $1.8 billion in June 1977 to $3.1 billion today, a 76 percent increase in less than two years.

When comparing nuclear power plants with other energy sources, the advocates of nuclear power have rather consistently failed to include the full costs. While all types of electrical generating plants have initially construction costs, nuclear power plants have the additional costs of disposing of radioactive wastes and of decommissioning worn-out plants. The cost of disposing of the flow of radioactive waste generated by nuclear power plants cannot be estimated because an acceptable plan for disposing of it does not yet exist. Waste is currently being stored in temporary facilities, pending the development of a permanent means of disposal.

Estimates of the cost of decommissioning worn-out nuclear power plants, which remain intensely radioactive for years after they are closed down, range from $50 to $100 million per plant. The cost of decommissioning the defunct West Valley nuclear fuel reprocessing plant in New York State ranges from an estimated $650 million to $1 billion. The federal government and the state government of New York may be negotiating for some time on who is responsible for the cleanup. But in the end, all of us will pay the bill either as consumers of electrical power or as taxpayers.

The public opinion polls taken since Three Mile Island show a marked increase in those opposed to nuclear power among the public at large. But the strongest shift in public opinion may be occurring among the executives of the nation's utilities as they ponder the eventual outcome at Three Mile Island. The Nuclear Regulatory Commission has indicated that the Three Mile Island plant may be so badly contaminated that it will never again generate electricity. If it becomes a $1 billion mausoleum as Sen. Gary Hart suggests, the financial implications for General Public Utilities Corporation, which owns the plant, are grave indeed.

The week after the accident occurred, General Public Utilities announced that it was suspending construction immediately of a $1 billion, 1,1000-megawatt nuclear plant being built in Lacey Township iin New Jersey. To conserve scarce capital, the company is also halting construction on a smaller, coal-fired power plant in western Pennsylvania.

At a time of declining growth in the demand for electricity and of record interest rates, many utility executives will become increasingly reluctant to undergo the financial exposure that large nuclear plants entail. As plants age and as the radioactive waste in temporary storage accumulates, utility executives will be forced to take into account the back-end costs of nuclear power as well as the up-front costs common to all sources of energy.

The principal fallout from the Three Mile Island accident may not be the radioactivity emitted during late March and early April, but the economic reassessment of nuclear power that it leads to, not only in the United States but throughout the world.