Boom eases but expansion goes on

The United States economic recovery is no longer rocketing ahead, but it is still moving at a respectable clip. The economy grew at a 7 percent rate in the July to September period, according to the Commerce Department's preliminary estimate. The projection came on the heels of a torrid 9.7 percent expansion posted during the second quarter. Other recent statistics reinforce the impression that the economy is cooling off.

The rate of growth ''is somewhat slower than the initial burst but is still quite respectable,'' says Edgar Fiedler, economics vice-president at the Conference Board, a business research organization.

The slowdown has a silver lining, analysts say. It is being fed by a wider variety of sources - including capital spending and inventory building - than earlier in the year, thus making the rebound more durable. This was the first quarter since the recession began when companies, taken togther, increased their depleted stocks of goods waiting to be sold.

''The economy is coming out of the early recovery and into the expansion phase,'' says Alan Murray, vice-president and economist at New York's Citibank. ''That means a slower rate of increase but better balance.''

So far the recovery has been accompanied by less inflation than many economists expected. Prices in the third quarter are projected to rise 3.2 percent when measured by the broadest measure of inflation, the gross national product (GNP) implicit price deflator, the Commerce Department says. Prices rose 3.3 percent in the second quarter.

The economists surveyed by Blue Chip Economic Indicators, a newsletter published in Sedona, Ariz., expected prices measured by the deflator to rise 4.5 percent in this quarter.

''What is unusual about this recovery is that prices have increased so modestly compared with other recoveries,'' says Sandra Shaber, senior economist at Chase Econometrics, a forecasting firm.

Price increases are still being curtailed by excess capacity in many industries, economists say. ''There is a lot of slack in the economy, a lot of production capacity which is underutilized,'' notes Commerce Department economist Leo M. Bernstein.

In addition, unseasonably warm weather has caused a larger than expected cattle slaughter, which has helped contain food prices. But the resulting smaller herd may trigger higher beef prices next year.

Slower growth of consumer spending is the biggest factor behind the economy's less rapid gains, economists say. For example, personal spending dipped 0.3 percent in August, the second monthly decline in a row and the largest since October 1981. Part of the August drop was the result of automakers running short of popular 1983 models as their production cycle ended.

Looking to later revisions of the GNP numbers, Robert F. Wescott, an economist at Wharton Econometric Forecasting Associates, says, ''We are thinking of revising our third-quarter GNP estimate down to 6.5 percent (from 7.8 percent), due to consumer weakness.''

Consumer spending has been boosted this quarter by several nonrecurring factors, including pent-up demand as the recession ended and spending that anticipated the July 1 reduction in federal tax rates.

At least in the short term, the recovery is not imperiled by interest rates or credit market conditions, economists say. Interest rates ''will be relatively stable'' for the next four or five months, predicts Robert Gough, senior vice-president at Data Resources Inc., another forecasting firm. Private-sector demand for credit is still relatively weak, he explains.

In fact, credit market conditions prompted stock traders to push the Dow Jones industrial average to a new high of 1,249.19 Tuesday. Traders were buoyed by signs the Federal Reserve Board had increased the supply of credit, thus putting downward pressure on the sensitive federal funds rate, the rate banks charge one another for overnight loans.

Over the longer term economists warn that there is still a danger that looming federal budget deficts will collide with private credit demands, as the recovery continues and capital spending plans gain momentum. The result could be an interest-rate spiral. Next year, though, the Blue Chip forecasters expect 90 -day Treasury bills to average 8.7 percent, down from the current 8.99 percent level.

Exports remain a weak spot in the economy. The GNP estimate for the third quarter noted that exports continued to deteriorate. The main problem is a strong dollar, which makes US goods less appealing overseas. The resulting deficit in US merchandise trade is estimated at $60 billion to $70 billion for 1983 and $100 billion for '84.

Still, at the moment the economy seems poised to aid Ronald Reagan if he chooses to make a reelection bid.