Despite record amounts of electricity used to cool off an overheated America this summer, the utility industry expects the 1980 growth in demand to be the lowest of the past five years.

This paradox is partly the product of a recessionary economy combined with a warm winter and partly the result of the complex attitude Americans have toward energy conservation.

For the industry, it will be another record year. Already the country has used more power than in all of 1971 -- nearly 1.5 trillion kilowatt hours -- and has spent $66 billion for it, more than twice as much as the 1971 sales. But overall demand is up only 0.8 percent from last year, the lowest rate of increase since 1975.

This is in spite of a summer that shattered the previous power generation record set last year. In the record week ending July 19, the country's utilities sold 52.6 billion kilowatt hours of power, enough to light up all the canyons of New York City for two years.

The previous high of 49.516 billion kilowatt hours, set the week of Aug. 11, 1979, was surpassed every week from July 19 through Aug. 16 this year, when record heat scorched the South and Southwest. In that week power was flowing to the nation's air conditioners at a rate 14 percent above 1979 levels.

But still the year's total rise in demand will barely hit 2.5 percent, according to Jack Schenck, vice president for economic policy analysis at the Edison Electric Institute, the utility trade group that supplied most of these figures.

"You can't divorce electricity growth from economic growth," he said. "The real gross national product growth in the second quarter of this year was a negative 9 percent."

A slowed economy, he said, means a slower demand for electricity by industries working shorter hours to make fewer products. That slowdown cancels out many of the air conditioners working overtime.

A warm winter also canceled out much of the hot summer. If the electricity demand graph looked like Mount Everest in July, it was the Grand Canyon in January and February when homeowners used 4.5 percent less power than in 1979.

Conservation has also played a part, but how much is not certain.

Before the 1973 Arab oil embargo, electricity use was growing at the rate of 6 to 8 percent each year. Utilities embarked on crash construction programs to meet what they foresaw as major demand pressures by 1980. But when the embargo tripled oil prices, the economy choked. The soaring electricity demand halted, actually declining slightly in 1974.

The 1975 recession held the growth rate down, but in 1976 things appeared to be back to normal and power sales increased 6.7 percent. Building plans resumed.

Rising prices, however, had sparked a conservation movement. Electricity sales have been lower than expected every year since then, even when the economy seemed to be moving forward. As one result, much of the capacity that was planned and under construction before the energy crisis hit is now not needed -- except in summers like this one.

Nationwide reserves are about 25 to 30 percent more than routine demand, although estimates vary. The building boom has all but halted and no new power plants have been ordered in the last six months. Most utility people warn, however, that demand peaks like this summer's could cause problems in the future.

"It's the one-terrible-day problem," said Alden Meyer of the Environmental Action Coalition, which is critical of utility financing and construction operations.

That, he said, occurs when people who have virtuously sweated through the summer in order to save electricity all decide on one awful day that they have sacrificed enough and can afford to cool off just this once. When they punch the "on" button simultaneously, the demand for power skyrockets. Utilities in the past have built power plants for just this moment, and many of them stand idle much of the time. Customers, of course, bear the costs.

In the dog days this summer in Texas, one of the states hardest hit by the record heat, peak demand on that worst day reached 31,200 megawatts, far and away a record. But the state has a capacity of 42,000 megawatts, or an excess of 24 percent over even that worst-case event, according to EEI figures.

Customers are now paying more for electricity than ever before. A kilowatt hour that cost a nationwide average of 1.67 cents in 1970 jumped to 2.5 cents in 1974 and 3.97 cents last year, according to Tom Woods of the Energy Information Administration in the Department of Energy. This year the price is expected to be about 4.5 cents.