The American economy continues to present a puzzling statistical face to the world.

Last week the Commerce Department estimated that the gross national product, adjusted for inflation, rose at a 3.2 percent annual rate in the first quarter, the best pace in a year.

But only a day earlier, the Federal Reserve said that U.S. industrial production fell in March for the second month in a row. The output of the nation's factories, mines and utilities was only 0.3 percent higher in the first quarter than in the final three months of 1985.

New housing construction has been strong: Starts of new units have been running well above an annual rate of 1.9 million for the third consecutive month. With mortgage interest rates at the their lowest levels in years, most analysts expect the housing market to stay healthy in most of the country.

But the business portion of the investment picture is far from rosy. Collapsing spending on exploration and development of oil and gas wells helped to push overall business investment other than for inventories down at nearly a 14 percent annual rate in the first quarter. In addition, the latest Commerce survey shows that businesses plan to spend only about 1 percent more this year in real terms than they did in 1985.

As for business inventories, part of the rise in the first quarter -- particularly in the automobile industry -- was involuntary as sales fell sharply behind production. "The evidence on lead times, deliveries and order backlogs doesn't suggest that there is any acceleration in inventory accumulation," said economist Alan Greenspan of Townsend-Greenspan and Co.

Meanwhile, prospects for the U.S. trade balance remain murky. Some analysts believe that the improvement in trade shown in the GNP accounts for the first quarter will turn out to be somewhat smaller than was estimated by Commerce statisticians working with only January data that, in turn, are subject to revisions.

Federal, state and local government spending, which accounts for about 20 percent of GNP, isn't likely to be growing rapidly. Federal government outlays are being constrained by cuts already required under the Gramm-Rudman-Hollings deficit reduction law, and several states such as Louisiana, Texas, Oklahoma and Alaska are cutting their planned budgets because of falling revenues from taxes on oil and gas production.

That leaves the biggest piece of GNP: personal consumption spending, which was nearly 65 percent of the total in the first quarter. About half of all such consumer spending is for services and tends not to vary as much as that for goods, particularly for durables such as autos. Spending for nondurable goods rose at a hefty 7.7 percent annual rate in the first quarter, while that for services went up at a 3.4 percent rate and that for durables fell at a 1.5 percent rate.

What consumers will do next is unclear. Some forecasters believe that declining oil prices will encourage them to keep increasing their outlays at a good clip. Others, pointing to consumers' high and rising debt load, believe that they will be more cautious, especially because personal incomes are going up at only a moderate rate.

So what does all this add up to? "The economy is sluggish at the moment and showing very little sign of a pickup," Greenspan said. "On the other hand, it is not contracting. It is a case of quintessential dullness."

Brothers David A. Levy and S. Jay Levy, two well-known forecasters based in Chappaqua, N.Y., assessed the outlook this way: "As long as swings in currencies and oil prices are playing capriciously with the outlook for the trade deficit, and as long as listless capital and inventory investment are having little effect on growth, the economy will be capable of either accelerating or contracting abruptly. This unprecedented, unsettled situation is not likely to endure for long."

Without a substantial improvement in the trade deficit and robust consumer spending -- which will require keeping personal saving as a share of disposable personal income at low levels -- 1986 will not turn out to be a good year economically, the Levys predict.

Most forecasters seem to be convinced that those and other good things will come to pass. Edward Guay, chief economist of CIGNA Corp., is one who does.

Pointing to the substantial increase in financial assets and cash in the economy, Guay wrote recently, the "liquidity is still accumulating. It will eventually lead to a sharp increase in economic activity. Those who have gained from lower energy prices will soon be spending more. Those who gain from lower interest rates will soon be spending more, or interest rates will keep falling until they do. Also, the shock to the energy industries will be absorbed and the cutbacks will be completed."

Once all that has happened, "Sales and orders will improve, production and operating rates will rise, and active credit demands will emerge," Guay said. "We will begin to consume some of the liquidity which has been created during the past year."

In the meantime, look for more of that "quintessential dullness."