Economic trends send out puzzling signals for US businesses and consumers

The economy is sending consumers mixed signals on three pocketbook issues: inflation, income, and interest rates. Spurred by sharply higher vegetable prices, the August Consumer Price Index rose a seasonally adjusted 0.5 percent, the sharpest rise since April. For the first eight months of the year the index has risen 4.2 percent. If the August pace were to continue, however, inflation would be running at a 5.5 percent rate.

''I don't think we should be too worried'' about the August uptick, says David Wyss, senior vice-president of Data Resources Inc., an economic consulting firm. Much of the hike does not reflect underlying inflation, he says, but rather volatile changes in farm prices and certain problems in adjusting home fuel prices for seasonal factors, among other influences.

Consumer prices are expected to rise about 3.9 percent in 1984 and climb 4.2 percent in '85.

Analysts say the recent contract hammered out between General Motors Corporation and the United Automobile Workers will help keep inflation under control and restrain upward pressure on wages. Full details of the contract have not been publicly released.

Based on reports of a settlement providing an 8.5 percent wage hike spread over three years, the agreement is ''shockingly moderate,'' says David Jones, an economist with Aubrey G. Lanston & Co., a government securities firm. ''Wage pressure will remain moderate and productivity growth will be stronger than is typical for this stage of a recovery (due to other contract provisions) and that will keep pressure off inflation,'' he said.

Based on this optimistic longer-term price outlook, many firms are planning salary increases for 1985 which look modest compared with the double-digit increases salaried employees received as recently as '81. A survey of 689 companies by Hewitt Associates, a Lincolnshire, Ill., compensation consulting firm, shows major companies are planning to give increases averaging 6.2 percent in '85, the same size salary hikes they gave this year.

But the salary increases ''will be greater than the rate of increase in consumer prices, '' notes John Linton, a partner at Hay Management Consultants, and thus workers will enjoy an increase in their buying power.

But with companies planning to hold 1985 salary hikes to the same level as 1984 pay hikes and inflation expected to accelerate next year, workers may gain less economic ground in '85 than in '84.

Labor Departent figures released Sept. 21 showed that the average worker's inflation-adjusted earnings in August fell 1 percent from July after adjustment for seasonal factors.

One signal late last week that consumers might face slightly lower interest rates was Morgan Guaranty Trust's reduction Friday of its prime interest rate by a quarter-point, from 13 to 12.75 percent. Morgan is the nation's fifth-largest bank.

The prime is a benchmark lending rate that banks use to set the cost of loans to corporate customers. Consumer lending rates are not directly tied to the prime but often move, with a time lag, in the same direction.

No other major money center bank followed Morgan's lead, although several regional banks did.

Partly in reaction to the prime's decline, the dollar fell sharply on Friday. It had been trading at record highs. The higher US interest rates, the more attractive investments in dollars are for foreigners. The dollar's drop helped push up interest rates in the bond market as traders worried that the Federal Reserve would tighten credit conditions to support the greenback. A falling dollar also could add upward pressure to consumer prices by boosting the price of imports.

''I wouldn't be surprised if no (big bank) followed and Morgan's prime was back to 13 within a week,'' said Bernard Markstein III of Chase Econometrics, a consulting firm.

A key reason Morgan lowered its prime rate, analysts say, is that the federal funds rate, the rate banks charge each other for overnight loans, recently has declined. Since the federal funds rate influences the cost of money a bank lends to customers, a decline can prompt banks to lower their prime rates.

But Mr. Markstein asserts that the funds rate has fallen because the Federal Reserve Board has increased the supply of money in the economy for technical reasons and that the increase could be reversed in the near term, sending the federal funds rate back up.

That view is not shared by Aubrey Lanston's Mr. Jones, who sees other major banks falling into line with Morgan and expects the prime to drop to 12 percent by the end of 1984.

He bases that forecast on the belief that the Fed has acted to ease credit conditions, not just moved to make technical corrections. And he adds that banks also are likely to lower their prime lending rates to win back corporate customers. In the past two months corporate loan demand has been weak although it rose last week.

One chart: Average Salary Increases. 1980-1985. Source: Hewitt Associates.

Percent

1980 9.5 %

1981 10.1

1982 8.5

1983 6.3

1984 6.2

1985 6.2*

*Estimated