A proposal requiring popular approval for the construction of power plants was defeated yesterday in a nationwide referendum, Washington Post special correspondent Jonathan Rollow reported.

Government warnings about the "grave consequences" for Switzerland's economy won out over a campaign by ecological and antinuclear groups citing the possible health and environmental hazards of nuclear power.

More than 1.8 million voters went to the polls, a heavy turnout. They rejected the antinuclear proposal by 51.2 percent. The proposal was also defeated in individual cantons, 14 to 9.

The defeated proposal would have set rigid conditions for the licensing of nuclear installations which, the government feared, could have halted nuclear projects in the country. In addition, the proposal required that each nuclear construction project receive popular approval in regional votes in the communities and neighboring areas concerned.

As the debate over nuclear energy has heated up in the United States and Western European countries, the vote in Switzerland attracted international attention. The outcome of the vote runs counter to a referendum in Austria last November that blocked the government's plan to operate a nuclear power plant.

The government warned against future energy shortages and unemployment. Events in Iran boosted the government's case. Swiss dependence on imported oil has been acutely felt by Swiss consumers who have had to pay 70 percent more for heating oil since the halt in Iran's exports.

As part of its overall plan to solve the energy crisis, the government wants nuclear energy to meet 13 percent of the nation's energy needs by the end of the century. Expensive imported petroleum currently accounts for 76 percent of Swiss energy consumption and nuclear energy 3 percent.

Significantly, the antinuclear proposal was rejected in most of the communities which either have or are scheduled to have nuclear power installations.