Time was when conventional wisdom held that economic expansion couldn't occur without a parallel rise in energy consumption.

Since the OPEC-induced oil shortages of the 1970s, that relationship has been proven infinitely more flexible than had been thought.Between 1973 and 1986, the U.S. economy grew by more than a third. Energy consumption during that same period, however, didn't grow at all.

But in the last two years, as world prices have slumped, the United States has rediscovered its expensive, self-destructive taste for oil.

To those who bewail our once-again growing dependence on imports, the answer is not to drain America first, exploring for oil in the Arctic National Wildlife Refuge. All this would accomplish on the off chance oil would be found there would be the postponement of the final day of reckoning with our profligate habits.

Nor is the solution increased reliance on nuclear energy, which is not only far more costly than oil when costs of construction and waste-management are factored in, but far riskier for public health.

Nor, finally, is the answer to be found underground, in the nation's abundant coal reserves. More and more, research on acid rain leaves little room for those who argue that damage to Eastern forests is unconnected to coal burned in the Midwest.

What is the answer? It is chiefly conservation. After all, it was conservation everything from mandated fuel efficiency standards for automobiles and lowered speed limits to incentives for home insulation and the like that was responsible for the flat rate of energy consumption from 1973 to 1986.

As shown by Europeans and Japanese, who consume 40 percent less energy than Americans on a per-capita basis, there is no connection between enjoyment of the perquisites of industrialized civilization and high levels of energy use.

Unfortunately, the Reagan administration has not taken the lead in putting the United States back on a conserving course.

The Energy Department's budget request for fiscal 1989 calls for $86.3 million for conservation research and development one-half of 1 percent of the $16 billion it hopes to receive.

True national security comes not with ensuring continued oil supplies but in reducing our overall consumption of energy in the first place.