Back in 1966, the Boeing Co. and Pan American World Airways announced that Pan Am would be the first customer for the jumbo 747 jet. That order launched the airline into a new era.

It was a disaster. Too much airplane, too soon.

McDonnell Douglas and Lockheed followed with their own jumbos, and major airlines eagerly lined up to buy. They regretted it. Flying a lot of expensive, nearly empty planes is no one's idea of efficiency. Airlines' productivity and profits suffered. Only by the mid-1970s did traffic catch up with the airlines' bloated capacity.

What makes this episode worth recalling is the prevalent notion that, like a good 5-cent cigar, all this country needs is a big shot of investment. The hankering is natural enough. Productivity -- roughly the measure of output for each worker -- has stagnated for the past three years. The idea that more plant and machinery per worker ought to cure low productivity seems sensible and appealing.

Huge investment incentives, embodied in proposals for liberalized depreciation, constitute a central element of President Reagan's economic program. But investment is not necessarily a case of the more the merrier. Poor or premature investments, as in the case of the 747, are made all the time. Before throwing too much money at this problem, we ought to look closely at just what the problem is.

The notion that investment needs stimulating assumes that it has been badly lagging. This is exaggerated.

The table below shows business capital stock: that is, all the economy's factories, stores, office buildings, warehouses and machines. The first column lists the value of "gross" stock -- everything that's around -- and the second column gives the percentage change for the past four decades. The third and fourth columns give the "net" stock -- the gross minus an estimate of depreciation (or obsolescence) -- and percentage changes. All figures are in trillions of "constant 1972 dollars. [CHART OMITTED]

As shown by this table, the rate of business investment slowed during the 1970s but still did as well as or better than the 1940s and 1950s. Might the figures for the 1970s by bloated by pollution-control investments and other government-mandated spending? Perhaps, but not much.

Pollution-control spending has accounted for roughly 5 percent to 6 percent of business investment. Assuming all of that useless -- clearly an unwarranted assumption unless you think pollution makes life better -- shaves only 2 to 3 percentage points off the 45 percent increase over the past decade.

To a large extent, we are prisoners of images. The dominant images these days are of the automobile and steel industries. They're sick. It's easy to think that they've suffered from inadequate investment and, by extension, that all U.S. industry is in the same situation.

But the problems of the auto and steel industries go well beyond investment -- excessively high wages have overpriced their products and cost them sales -- and their problems don't necessarily reflect all of U.S. industry. McGraw-Hill, publisher of Business Week, periodically surveys business to find out what proportion of their plant and equipment they consider obsolete. In 1980, the answer was 11 percent, virtually the same as in 1970.

You also will hear that the United States invests less than other countries. The Treasury Department reports, for example, that Japan invested 33 percent of its gross national product in the 1970s compared with 18 percent for the United States.

No one has adequately explained these different levels, but the overall figures may conceal as much as they reveal. In 1978, for example, Japan divided its investment as follows: business plant and equipment amounted to 13.9 percent of GNP (United States: 11.2 percent); housing, 6.6 percent (United States: 5.2 percent); and government, 9.9 percent (United States: 2.1 percent.).

Japan's higher investment in housing and government -- roads, sewers, hospitals -- may mean its system of public services is less developed than in the United States. But two other factors further blur the meaning of these figures. First, perhaps a third of government investment in Japan (telephones, railroads) would be considered "private" in the United States; and second, one large U.S. government investment (in military hardware) isn't counted in any of the statistics.

None of this is intended as an argument against more investment. Higher inflation rates have eroded the worth of existing depreciation write-offs, which are based on original purchase costs and therefore aren't adequate to buy replacement plant and equipment at higher prices. And environmental requirements and higher energy prices have created additional investment demand.

But we need to be cautious. The simplest explanation (and, no doubt, an inadequate one) for lagging productivity in the 1970s is that the work force exploded with the flood of the "baby boom" generation into jobs. Labor became more abundant in relation to capital, and productivity was affected accordingly. In the 1980s, as labor force increases slow down, the situation could reverse.

Harvard economics professor Dale W. Jorgenson thinks that the administration's depreciation proposal provides tax benefits so generous that firms might profit by making investments even if they sit idle. This is nothing if not inefficient. Treasury officials disagree strongly, arguing that the existing tax system is heavily biased against investment.

Congress shouldn't be frightened away from this issue by its addmittedly intimidating technicalities. Just because some additional investment might be beneficial doesn't mean that all investment is -- that any measure that purports to promote investment is automatically a good one.