Rising temperatures across America are overwhelming vulnerable people and could kill thousands, according to an authority on health and the environment.

"This will probably emerge as one of the largest natural disasters of this century . . . and it will have just whispered its way by," said W. Moulton Avery, executive director of the Center for Environmental Physiology in Washington.By ones and twos, the poor and elderly are succumbing to the heat, which overtaxes their bodies, he said. But most of these tragedies will pass with little notice, being recorded in government statistics as heart attacks or strokes, rather than heat-related fatalities.

In the end, Avery warned Tuesday, this summer's stifling temperatures threaten to exact a higher death toll than the 1980 heat wave that killed an estimated 15,000 Americans,

"If I had in my hand right now the number of people that have died this summer (from heat) it would be front-page news all over the country, but I don't have that number," said Avery, whose non-profit center researches the effects of heat and cold on humans for government agencies and other clients.

He has argued for a reporting system to record heat deaths, but statisticians must depend on comparing deaths during heat wave years with "normal" years and calculating the excess fatalities. That was the system used to determine the 15,000 extra deaths in 1980.

"What we're living through now is the same thing we were living through in 1980" and is worse than many other hot summers, he said.

Normal death rates nearly doubled from Oklahoma east during a 1966 heat wave - with deaths jumping to five times normal in St. Louis - according to the National Oceanic and Atmospheric Administration.

The Senate Special Committee on Aging later reported that heat waves in 1963 and 1966 claimed a total of 11,000 lives.