The U.S. economy seems to pay little attention to warnings of its imminent collapse.

Anyone with a taste for doomsday narratives can choose from a variety of theories of why we should brace for the end of prosperity as most of us have known it. The stock market panic of last October signaled to some that the somber day was at hand.But here we are approaching the 70th consecutive month of economic growth, after a first quarter in which the gross national product expanded at a robust annual rate of 3.9 percent. Other key figures suggest a bustling climate for months to come. Experts are revising their 1988 growth forecasts upward.

Unemployment nationally, at 5.6 percent, is within a tenth of a point of the 14-year low reached in April.

The industrial sector particularly is readying for busier times, attributed largely to increased demand for exports. The trade deficit - chronically one of the scarier statistics - was at a three-year low in March, reflecting greater U.S. competitiveness abroad. Factory construction in this country now is up 39 percent over last year, and machine-tool orders in April were 94 percent greater than in April of 1987 - both forerunners of stronger industrial labor demand.

The latest set of "leading indicators" supports an expectation of continuing growth, though at a slower pace than that of January-March.

People who insist on the inevitability of recession, in the normal cycle of things, are now postponing the envisioned downturn until sometime next year, after a new president has been picked in an election influenced by this year's steady growth.

But by then, it is possible that a lot more factory workers will be earning and spending paychecks, foreign commerce could be making greater demands on U.S. production and the economy even then might not be ready to lie down. It has happened that way before.