Perhaps it is the fact that summer is finally in the air - officially as well as measured by soaring temperatures in parts of the United States. But the news out of Washington of the robust 6.6 percent US economic growth rate projected for the April-to-June period is the type of heartening report that cannot help but bring a sense of cheer, no matter what the calendar says. Now the unmistakable task for political leaders - and the public - is to nurture and protect such a vigorous recovery.
As noted by Roger Smith, chairman of General Motors Corporation, the latest growth forecast - the so-called ''flash'' estimate of the nation's gross national product (GNP) - is ''good news'' to an economy that has been mired in recession, an unemployment rate that is now 10.1 per-cent, and interest rates that remain too high. The projected growth rate for the second quarter of this year compares to a stodgy 2.6 percent rate for the first quarter, and a sluggish 1.7 percent increase for all of 1982.
Does that mean that the entire year will turn in such a rousing 6.6 percent increase? Probably not. The sharp hike in the second quarter is largely the result of a slowdown in the rate of inventory cutting by businesses, which means that many firms had to step up production of new products. Still, the economic consensus suggests that the year will show solid growth and probably above the administration's own forecast of 4.7 percent.
What must not be forgotten in all the euphoria, however, is that a sustained growth in the US economy is linked to the rising prosperity of America's industrial allies as well as that of the third world.
In this regard, the steps necessary to ensure a sustained recovery seem clear:
* The US must lower interest rates. We are not talking here about overall, or general, interest rates. Rather, the issue is what economists call ''real'' interest rates - that is, the cost of borrowing money after subtracting out the rate of inflation. Real interest rates remain historically high and thus constitute an impediment to consumer purchases of such big ticket items as houses, cars, appliances, etc. Congress and the administration must use the spending restraint and tax hikes necessary to hold down the size of the federal deficit so that the government will not have to massively intervene in money markets and crowd out private borrowing over the next several years.
* The US must take all appropriate steps to ensure maximum possible world trade. Private and governmental loan dollars will still need to be made available to third-world nations, with which the US now conducts a substantial portion of its overall trade. And the US and its major industrial trading partners must avoid protectionist measures.
* Finally, Congress and the administration must not overlook the need to aid those persons who have now been out of work for many months in finding new jobs. That does not mean that this is the time for ambitious new jobs programs, although many new federally financed jobs are coming on line because of earlier federal jobs plans. What is important is that many unemployed persons who are now expected to return to the labor force in search of work because of improving economic conditions be given direction and assistance to help match workers with new positions. Private industry and the government can surely undertake such initiatives under existing manpower and Commerce Department programs.
Thus there are still a number of economic challenges facing the US. But, at the same time, all Americans can momentarily bask in the glow of summer - and a resurgent economy.