Financial realities have done what protesters never could--stopped growth of the nuclear power industry in its tracks. No applications to build a new nuclear power plant have been filed with the Nuclear Regulatory Commission since 1978, and numerous projects have been dropped or deferred.

Supporters of the industry blame the shutdown on the general malaise of the economy and warn of a shortage of generating capacity in the future when demand grows.

But its critics blame at least part of the industry's problems on poor cost control and greater than anticipated operating costs in an immature industry. Utilities with nuclear power plants, for instance, have had to replace costly steam generating equipment that had been expected to last the life of the plants. In addition, considerable uncertainty surrounds future outlays, including the costs of waste disposal, and what can be done with the units at the end of their useful lives.

In the past several years the industry has been battered by cost overruns, the high price of financing, a slowdown in growth and newly discovered operating expenses.

In one of the most dramatic and costly cancellations, the board of the Washington Public Power Supply System announced two months ago it would terminate work on two of five nuclear power plants under construction, writing off the $2.25 billion already spent.

Construction cost estimates of the five WPPSS nuclear plants (which friends and foes of nuclear power alike describe as plagued by peculiar problems) soared from $4.1 billion to nearly $23.8 billion.

The month before the cancellation was announced, the Oklahoma Corporation Commission ordered that no further funds from customers of the Public Service Co. of Oklahoma be spent on the Black Fox nuclear power plant. The commission said that, notwithstanding the $200 million aready expended, the plant was "no longer economically viable."

The same day Standard & Poor's Corp. reduced the bond rating of the Public Service Co. of New Hampshire, raising additional questions about the fate of one of two nuclear power plants being built at Seabrook, N.H., although work is continuing.

In 1980, 16 reactors were cancelled and 70 delayed. In 1981, six were cancelled and 44 deferred.

So bleak is the outlook that General Electric Co. has said it expects no more domestic orders in this decade for steam generating equipment for nuclear reactors. "GE has not decided to abandon the nuclear market. The nuclear reactor market has left suppliers, rather than the other way around," said a GE spokesman.

"Nuclear power has become an investment with tremendous financial risks to utilities, and the utility industry itself is in such poor financial health it can no longer afford to purchase nuclear generating stations," Booz Allen & Hamilton Senior Associate John O. Sillin told a meeting of chemical engineers last fall. Financial markets have reacted by downgrading utility bond ratings and paying less for utility stock, which then makes it even harder for utilities to raise money.

A 1,200 megawatt nuclear unit going into service in the early 1990s will cost over $3.2 billion, Sillin said, noting that the figure represents nearly a tenfold increase in price since the early 1970s. "The average asset size of the 35 largest electric utility companies in 1980 was $5.2 billion," he added.

The perception of risk--much higher since the accident at Three Mile Island--has caused investors to require a premium on their investment, according to a bank official closely familiar with the Three Mile Island situation and the nuclear industry.

"In my opinion, we really don't have a nuclear option," he said. "The only thing keeping the industry alive is some foreign orders." There are 72 operating nuclear plants in this country.

"In elementary terms, it's the same thing that's wrong with autos, steel mills, housing and other industries--high interest rates," according to Carl Walske, president of the Atomic Industrial Forum. But utilities, and particularly the nuclear side of utilities, face additional problems.

These are compounded by the capital intensive nature of the industry, Walske said. For utilities, each $4 in capital expenditures equals $1 in revenue, compared with a $1-to-$1 ratio for steel, for example.

Utilities also have to live with the fact that returns on investment are spread over a long period of time and with the political nature of regulatory agencies, he said.

"The utility commissions . . . are responsive to the consumer. They were invented to protect the consumer," said Walske.

"What happens is that in times of high inflation, high interest rates and greatly increasing costs, the utility commissions find it difficult to jack the prices up fast enough to keep the utilities whole."

Walske warned that the reduction in construction of generating capacity now will leave the nation short of the power it needs when the economy improves and demand begins to grow more rapidly.

When utilities want to build nuclear power plants, they face an unpredictable licensing process that drags out construction time and subjects the projects to rapid inflation in construction costs, according to Walske.

Not everyone agrees that administrative delay is a major cause of the industry's problems, however. A report by the House environment, energy and natural resources subcommittee headed by Rep. Toby Moffett (D-Conn.) stated that bureaucratic delay was exaggerated by the industry.

"If the nuclear industry's candid concern is to protect consumers from unnecessary expense related to the nuclear generation of electricity, it would be well-advised to recognize that, when viewed in perspective, the greater economic threat to consumers is from design defects and utility errors that result in accidents--not from the comparatively minor costs of administrative delay," according to the subcommittee's report.

A surprising problem the relatively young industry discovered is that steam generating equipment that had been expected to last the life of the reactors doesn't. The result is expensive repairs.

"The steam generator repairs are extremely expensive, partly because of the radioactivity" that requires a large number of workers so that the exposure of any one individual is kept low, said Stewart Udell of the antinuclear group Critical Mass. Of 45 pressurized water reactors, 39 have had problems with that equipment, he noted. Of the ones that have not, five of the six only began operating in the past two years, he said.

Another potential problem is embrittlement--the premature aging of the vessel that holds the reactor core. The question is to what extent this weakens the vessel.

Still another cost looming for the industry is the price of decommissioning the plants at the end of their lives. Those costs--largely undefined--include decontaminating or securing the site.

"It's a lot different from the rosy future of having energy too cheap to measure," Udell said.