THE industrial world's economic recovery has become a long-lived patriarch. In the United States - the key power among industrial nations - it is now in its 49th month. This is only the seventh expansion to reach its fifth birthday in American history, and it still shows considerable vitality. Economists reckon it has at least a year to go.
Internationally, the recovery continues as well.
``It is a fairly bright worldwide situation,'' says Geoffrey H. Moore, director of Columbia University's Center for International Business Cycle Research, which compiles leading indicators for the economies of nine nations.
Reviewing history, Dr. Moore says the US enjoyed a six-year recovery starting in 1790, a 48-month one beginning in 1848, 50 months from 1932, 80 months from 1938 through World War II, 106 months beginning in 1961, and 58 months running from 1975.
Such long recoveries have become more frequent in modern times. Perhaps governments have learned something about economic management.
Overseas, the expansion in Japan and Australia had been showing signs of stalling earlier this year, but recent figures look better. The other countries on the list - Canada, West Germany, France, the United Kingdon, Italy, and Taiwan - all look promising.
So far, the US expansion, measured by real gross national output (the total output of goods and services in uninflated terms) has been somewhat below average, says Moore.
Economist F.Thomas Juster of the University of Michigan has looked at the pattern of the economy under six post-World War II administrations in ``Economic Outlook USA,'' published by his university's Survey Research Center.
Examining average annual growth rates for real GNP, the Reagan administration comes out with a middling performance. Here are the numbers: Truman (5.7 percent), Eisenhower (2 percent), Kennedy-Johnson (4.7 percent), Nixon-Ford (2.3 percent), Carter (2.9 percent), and Reagan (2.5 percent).
Of course, if the economy picks up its pace over the next two years, the Reagan record will improve.
One New York forecaster with a good record, Sam Nakagama, predicts American GNP growth will rebound to an annual rate of 4.9 percent in this fourth quarter and follow a quarterly pattern next year of 2.5 percent, 2.7 percent, 3.4 percent, and 3.5 percent.
The consensus among economists, however, is less cheerful. Blue Chip Economic Indicators of Sedona, Ariz., finds the average of several dozen forecasters is 2.6 percent next year. That same panel has inflation rising from 1.9 percent this year to 3.2 percent next year. Moore's leading index for inflation also shows an upturn.
So the period of relative price stability in the US may be ending. If inflation becomes bad enough, the Federal Reserve System will undoubtedly put on the monetary brakes and could bring the recovery to an end - say in 1988.
Blue Chip Economic Worldscan, looking at forecasts for nine nations and the US, agrees with Moore's optimism. Worldscan predicts GNP rising next year by 3 percent in West Germany, 2.6 percent in France, 2.5 percent in Britain, 2.9 percent in Italy, 5 percent in Brazil, 2.3 percent in Mexico (which was deep in recession this year), 3.1 percent in Japan, 2.1 percent in Australia, and 2.8 percent in Canada.
Editor Shea Smith III also notes that inflation is expected to be higher for these nations except Brazil, where it could be almost halved, to 61 percent. The Worldscan panel expects interest rate declines into the third quarter of 1987, followed by a rebound.