A chain reaction of events has put India's ambitious nuclear power program in a critical stage.
The Indian Atomic Energy Commission (AEC), which has been able to put only two commercial plants into operation over the past 25 years, plans to build 12 new reactor plants by the year 2000.
The cost of such a program, according to AEC chairman Homi Sethna, will be about $66 billion, or 50 percent more than the cost of planned oil exploration during the same period.
The chain reaction began in May 1974, when India announced a ''peaceful nuclear explosion,'' which also ignited a pullout of the United States and Canada from the Indian nuclear program. The American withdrawal left the 420 -megawatt plant at Tarapur running out of enriched uranium fuel, which may be gone by next year. Other foreign suppliers have not stepped in to help.
The Canadian exit was perhaps more damaging. Its reactor design relied on heavy water, not enriched uranium, and it has become the model for the ''Indianization'' of the nuclear program here.
''We don't import a thing for the program,'' Dr. Sethna says, although foreign observers doubt whether key parts, such as computer chips, are Indian-made. ''It's been a real struggle,'' he adds.
The struggle goes on. ''There's a price to pay if India continues to go it alone,'' an American official says. ''Japan was willing to buy all its technology, with no pride lost in receiving foreign help.''
The biggest hurdle is replacing the Canadian supply of heavy water. The Soviets have helped out a little, but India has chosen to build its own heavy-water plants, using two different techniques.
The first use of this water was to be at the Rajasthan atomic power station at Kota. Three other plants are in the works: a 470-megawatt plant near Madras is ''99 percent'' complete; a similar unit at Narora, in Uttar Pradesh State, is scheduled to go on line in 1986; and one at Kakrapar, in Gujarat State, is still on the drawing boards.
But the plant at Kota has been beset by problems. It runs at only about half of its 440-megawatt capacity. And with the Tarapur plant running at about half of its potential in order to save fuel, the Indian atomic power program is running in the 400-megawatt range.
That's a long way from the 10,000 megawatts planned by the Indian AEC for 18 years hence. With plants taking nine years or more to complete, the Ministry of Energy (which operates separately from the AEC) is counting on only 8,000 megawatts at best, with nuclear power supplying only 6 percent of India's electrical needs.
Meanwhile, the plants that produce heavy water for the nuclear industry are in hot water. The three plants at Baroda, Tuticorin, and Talcher use ammonia-hydrogen processes, and have had trouble because they are linked with a fertilizer-production process using gas. The other heavy-water plant, using a sulfide water-exchange process, has not worked well, because it runs off the distressed Kota plant.
Energy officials say coal plants can be cheaper than nuclear plants, if they are close enough to the mines. They can also be put into operation faster.
Nuclear plants might be more competitive, if they were on the scale of Western plants. But transporting equipment for larger plants is almost impossible in India where roads, bridges, and rail facilities can't take large loads.
''Our engineering costs are one-fifth cheaper than Western plants. But we get clobbered on transport,'' says Dr. Sethna.
India's electric grid, or network, also poses obstacles to bigger plants.
Voltage can sometimes fluctuate between 125 and 300, disrupting or even damaging a plant. For some time, only reactors generating 235 megawatts were possible. ''If we tried to run 800 megawatts, we just couldn't do it,'' said Dr. Sethna in an interview.
Is nuclear power worth the delays and the high costs, especially in a nation short on capital to help its poor? ''There's no other way out,'' Dr. Sethna states. ''If we waited one year, we'd be pushed back 10 years.''