Suddenly, the economy is posing a new concern: After five years in which the United States consumed more than it produced, Americans appear to be producing too much and consuming too little.

The development is arousing anxiety among Reagan administration officials, who fear the 1988 election year could be marred by a recession -- or at least a rise in unemployment -- that would damage the political fortunes of Republican candidates.

And at the Federal Reserve, officials who had confidently predicted a sound expansion in 1988 now see the need for lower interest rates to counter the possibility of a dangerous weakening in economic growth. Government officials disclosed late last week that the Fed probably would ease credit soon to ensure that interest rates continue their downward trend.

Paradoxically, the factors setting off the alarm bells arise from trends in the economy that most analysts welcome as healthy and necessary to reverse the nation's massive trade deficit.

American factories, responding in part to a surge in export orders, are operating at full throttle after a long period of decline. Consumers are starting to retrench after a five-year spending spree that sucked in hundreds of billions of dollars worth of imports.

But too much of a good thing can throw the economy off kilter. A government report released last Wednesday showed that businesses may have been churning out goods too rapidly during the final three months of 1987, at the same time that consumers were curbing their spending habits too vigorously.

The outcome was an accumulation of unsold goods on business shelves, and now economists are predicting that companies will cut output and employment in an effort to bring inventories into line with sales. The United States will be lucky to see its economy expand at a 1 percent annual rate in the first half of 1988, many analysts say -- a pace well below the levels needed to absorb job seekers into the work force.

"Unemployment is certainly going to slide up in the next few months," said Stephen Roach, senior economist at Morgan Stanley & Co. "It will be an uncomfortable prospect in an election year."

Nowhere is that discomfort felt more keenly than inside the administration, where a number of top officials, especially chief White House economist Beryl W. Sprinkel, are privately gloomy about the risks facing the economy. Sprinkel has been the point man in the administration's effort to prod the Fed to adopt stimulative policies.

"It's fortuitous that tax {revision} is going into effect this year; that may be the only thing that keeps us out of recession," one Reagan aide said. (The 1986 tax-law changes cut tax rates and reduced the burden on individuals.)

Most analysts are less pessimistic, arguing that the economy will avert a downturn in 1988 because it is drawing on new sources of strength. The main reason for hope, they say, is that while consumer spending is falling, demand from abroad for American products is picking up much of the slack.

"We've got a real export boom under way," said Lyle Gramley, chief economist for the Mortgage Bankers Association. Excluding farm products, exports rose at a sizzling 37 percent annual pace in the fourth quarter of 1987, Gramley noted. And consumer spending, while falling in the October-to-December period, didn't decline so disastrously as to make a slump in 1988 inevitable, he said. "Recession is a low probability -- one in four, maybe one in five," Gramley said.

A Fed official agreed: "With more growth coming from exports, it doesn't hurt to have dampened domestic demand in the United States," he said. In fact, the official added, a major slowdown in U.S. consumption is desirable because it will help shrink the trade deficit by stemming the flood of imports.

"This is what we need to make the trade adjustment," the official said.

In one sense, Republicans stand to benefit from what is going on in the economy. The export surge is reviving the very sectors that suffered for most of the post-1982 recovery -- smokestack industries in America's Rust Belt.

But administration officials, perhaps understandably in an election year, are nervous. They were already uneasy about the possibility of a new collapse in the dollar or the stock market, and now some of them fret that the economy is doomed to fare poorly in 1988 because, they say, the Fed kept interest rates too high and money-supply growth too low last year.

These officials gained only small comfort from reports late last week that the Fed is likely to ease credit soon. A change in interest rates usually affects the economy only after lags of several months or more, and the first half of 1988 appears all but certain to be sluggish.

The Fed's credit-loosening moves may help buoy the economy sometime in the fall, but the data showing a pickup would probably come too late to impress voters in November.

"Who cares about the third quarter?" one White House official asked, half-facetiously.