AMERICAN DEPENDENCE on imported oil has dropped substantially over the past two years. But it's not a bad idea to keep a wary eye on those figures.

The peak year for imports was 1977, when American oil consumption was rising rapidly and the Alaskan pipeline was just beginning to go into operation. At that point, imports were getting uncomfortably close to half of the total amount of oil used in this country. Currently, imports are down under one-fourth of total use. That level is perhaps deceptively low since the oil companies, under the pressure of high interest costs, have been running down their stocks. But even after accounting for this drawdown, it's clear that the trends are pointed in the right direction.

The basic relationship here is the amount of energy, from all sources, required to produce each dollar's worth of the economy's output. That crucial ratio has been dropping steadily and substantially ever since the first oil crisis in 1973. It's mainly a response to higher prices.

When American demand for energy drops, the impact falls entirely on the most expensive of the fuels--oil. When demand for oil drops, the impact falls entirely on the imports. Total energy consumption has been falling in this country for the past two years, and that reduction, although it might seem a relatively small percentage, translates into a very large drop in imported oil.

It is by no means certain that this progress will continue if oil prices keep falling. While lower prices are welcome at the moment when you pay your fuel bills, you might want to keep it in mind that American vulnerability to a foreign cutoff is still substantial. Even one-fourth of the country's oil supply is a very large flow, and any significant disruption of it would rapidly produce the familiar effects. Over the past couple of years Americans have proved to themselves that, without hardship or even great inconvenience, they can do with less oil. The case for continued caution and conservation remains compelling.