Indicators Up 1% in August, the Strongest Showing of ’93 : Forecast: The index’s broad-based gain may mean the economy is set to accelerate. Factory orders also increased.

The government’s economic forecasting gauge recorded its strongest gain of the year in August, suggesting an improving though hardly booming finish for 1993.

Meanwhile, factory orders increased during the month, pulled higher by aircraft and autos. And a private survey of corporate purchasing managers showed continued albeit slow improvement in manufacturing in September.

“We’re moving from very slow growth to moderate growth,” said economist Mark Zandi of Regional Economic Associates in West Chester, Pa. “The economy’s expanding, but not at a rate that will make us feel good.”

The index of leading indicators jumped 1% in August, flashing its most positive sign since December, the Commerce Department said Friday.

It was the third consecutive increase, following slight gains of 0.1% in both June and July.

Ten of the index’s 11 forward-looking indicators rose, the first time that many were up since December, 1986.

“The broad-based nature of the increase and the fact that it was relatively large is an encouraging sign and indicates the economy is set to accelerate as we move into the very important Christmas season,” Zandi said.

The economy, as measured by the gross domestic product--the total of goods and services produced in the United States--grew at a lackluster 1.4% annual rate during the first half of the year.

Zandi and most other analysts are expecting a growth rate between 2.5% and 3% during the second half. But they warn that won’t be good enough to produce a rapid increase in employment.

New orders to factories increased 0.9% in August to a seasonally adjusted $252.8 billion. But the backlog of unfilled orders slipped 0.6% to the lowest level since July, 1988. It was the sixth consecutive drop and the 21st in 24 months.

That’s a bad sign for employment at factories, said economist Lynn Reaser of First Interstate Bancorp of Los Angeles.

“It looks from the backlog like companies aren’t having very much difficulty completing orders with their existing work force,” she said.

In the first look at manufacturing in September, the National Assn. of Purchasing Management said its index of economic activity rose from 49.3% in August to 49.7% in September. A subindex on employment indicated jobs were declining in manufacturing, although at a slower rate than in August.

The government’s leading index is intended to forecast economic activity six to nine months in advance. The positive indicators are: a rise in building permits, a drop in applications for unemployment benefits, an increase in contracts and orders for new commercial buildings and business equipment, a lengthening of business delivery times, an advance in stock prices, an uptick in the average work week of factory employees, an increase in the backlog of unfilled orders for durable goods, a small rise in consumer confidence, a gain in new orders to factories for consumer goods and an increase in the prices of raw materials.

The only negative indicator was a decline in the inflation-adjusted money supply.