The weather last winter may have been cold, but the economy was hot, new government figures show. Real gross national product (GNP), the inflation-adjusted value of goods and services produced in the United States economy, roared ahead 8.3 percent in the first three months of 1984, after climbing 5 percent in the final quarter of 1983.
The robust performance surprised many analysts who had expected GNP to come in below the 7.2 percent first-quarter ''flash'' estimate released earlier. But strong consumer spending early in the quarter, coupled with robust business investment in inventories (supplies of goods waiting to be sold) made the first quarter the strongest since the 9.7 percent gain posted in the April-June period of 1983.
''Even though March was quite weak, if you draw a monthly pattern and start with two strong months, the average is still high,'' explains Steven Wood, senior economist at Chase Econometrics, a forecasting company. The new GNP figures do not include complete data for March and are subject to revision.
Neither consumer spending nor inventory building is expected to keep racing ahead at the pace that got 1984 off to such a strong start. At the same time, many analysts expect interest rates to inch up as the year goes on. As a result, most economists are calling for slower economic growth - and thus less rapid gains against unemployment - for the balance of the year.
''Real GNP will post average increases of 3.0 percent over the remaining three quarters of 1984,'' says Edward Yardeni, senior vice-president of Prudential-Bache Securities. ''That would be in line'' with growth in the same period in the past seven postwar recoveries, he says, and would mean the '84 economy grew 5.6 percent overall.
''We are going to have a good year, a healthy second year of expansion,'' adds Harold Nathan, senior financial economist at San Francisco's Wells Fargo Bank. He shares Mr. Yardeni's expectation of slowing growth as the year progresses, and expects 5.5 to 6.0 percent gain for 1984 as a whole.
These upbeat predictions - tempered as they are by expectations of gradually rising inflation and interest rates - could make the economy a less appealing subject for the Democratic presidential candidate chosen in July.
White House spokesman Larry Speakes said the GNP figures make it ''obvious the economy will remain strong, with low levels of inflation.''
''Ronald Reagan is in great shape with Main Street, but he's got to be worried about Wall Street,'' notes David Hale, chief economist at Kemper Financial Services in Chicago. In other words, rapidly rising interest rates or inflation could spoil voters' perceptions of the economy. Sharply falling bond or stock markets could shake voters' confidence about 1985, he says.
The big forecasting firms expect economic growth in 1985 will be sharply slower than in 1984, as interest rates rise and inflation accelerates.
Despite the strong pace of first-quarter growth, inflation was relatively well behaved from January through March. Prices as measured by the GNP implicit price deflator, which tracks changes in both prices and the mix of goods produced, rose 4.1 percent in the first quarter.
The relatively good price behavior has several causes. Economists say that as a result of the strong dollar, imports rose, and US goods thus faced strong competition from foreign goods which held down prices. Then, too, ''businesses have made great strides in cutting costs. They have made substantial productivity improvements,'' says John M. Albertine, president of the American Business Conference, a group of 100 fast-growing companies.
The first quarter's inflation rate of 4.1 percent ''is definitely a low rate by recent historical standards,'' says Citibank economist Rosemary Rinder. ''But we think inflation will accelerate very quickly'' and be running at a 7 percent pace (as measured by the GNP deflator) by the fourth quarter, she adds. Other analysts expect a somewhat slower inflationary pickup, with Wharton Econometric Forecasting Associates calling for inflation in 1984's fourth quarter to be running at 5.4 percent.
The upward pressure on prices will come from a variety of sources. As the economy continues to grow, lower unemployment rates give workers greater freedom to seek wage increases. And continued expansion also can lead to shortages of production capacity which put upward pressure on prices.
Economists are fairly sure the pace of growth will slow in 1984. ''Much of this (rapid growth) came from incredible pent-up demand from consumers in durables and housing,'' Mr. Albertine says. ''Obviously, that demand is being met and will diminish'' in the months ahead, he says. The March turndown in housing starts and retail sales - as well as much slower growth in auto sales and personal income - seems to confirm this.
And more than half of the first-quarter increase in GNP was the result of business inventory building, notes Citbank economist Rinder. ''Not in the wildest stretch of the imagination could that be prolonged,'' she says.
In essence, companies were rebuilding inventories from very low levels. And farm inventories rose due to the government's payment-in-kind program. Without adequate inventories, a company can lose sales and market share.