Washington — After hitting the trough of the worst recession since the 1930s, the US economy is rebuilding in a normal manner. The nation's gross national product (GNP) - a measure of the total goods and services produced in the economy - is increasing at a healthy 4 percent rate, according to a ''flash'' projection by the US Commerce Department.
The flash projection is based on partial data. But if it holds up, it will be the strongest quarter in two years. Back in 1981 the comparable quarter gained 7 .9 percent but then the recession set in.
The US isn't out of the woods yet, say economists, who note that unemployment is 10.4 percent.
But White House spokesman Larry Speakes said of latest Commerce Department figures: ''We are moving toward an excellent recovery from the recession. It's the most conclusive indication that we have received that the economic recovery has begun and is proceeding at a healthy rate.''
With this announcement came welcome news from Wall Street that the Bank of New York had cut its rate on consumer loans, effective March 23. A homeowner who wants to borrow money for home improvements will find interest down to 14.5 percent from 16.5 percent for 48 months or less, and 15 percent for longer loans.
Used car rates are also cut - 2 points to 14.5 percent for newer models, and down to 16 percent on 1975 and earlier models.
Developments come at a critical moment. At home, President Reagan debates whether to reappoint Federal Reserve Board chairman Paul A. Volcker in August. The Fed must guide the money markets through what could be a new bout with inflation as the economy improves. Abroad, the 10-nation European Community's finance ministers reached a crisis in Brussels in a test of wills between France and West Germany over currency values.
Behind developing global problems is the Western economic summit conference set for Williamsburg, Va., in May, which will consider trade relations with the Soviet Union.
Economists inside and outside of the administration watch figures with deepest interest for trends. The new figures are at the high end of forecasts; they seem to substantiate a moderately strong recovery.
How bad was the 1982 recession? It was the worst since the economy slumped in the demobilization period after World War II.
How do new figures affect unemployment? Economists say 3 to 5 percent growth in GNP must be sustained for more than a quarter before unemployment improves.
There's another factor: consumers have been holding back on spending, it is declared. If encouraged they may go out and buy that new car or kitchen sink. So far unemployment has checked consumers.
A Morgan Guaranty Trust Company of New York monthly survey now forecasts an increase in real GNP this quarter of 4.7 percent, at an annual rate, compared with 3.8 percent forecast last month. Better economic prospects find their way into political debates in Washington. Some of the biggest decisions on taxes and budget are pending.