One of the first reports on the state of the economy in December indicates that it expanded briskly, another piece of evidence that the October stock market collapse has had little impact on economic growth.

A monthly survey of purchasing managers for manufacturing companies found faster growth in December, compared with November, in both new orders and production. Robert J. Bretz, director of materials management at Pitney Bowes Inc., said the rise in new orders in particular foretold continued expansion.

"New orders themselves are the trigger for increased production in the future," he said. "What this portends is a relatively strong production month for January and carrying into future months."

The survey, done by the National Association of Purchasing Management, is considered a reliable indicator of economic trends because purchasing managers -- more than 250 are surveyed each month -- are in a position to watch employment, production plans, prices and inventories before those statistics are compiled by government agencies.

Following the sharp decline in the stock market on Oct. 19, when the Dow Jones industrial average fell 508 points, economists predicted that consumers would reduce their spending, slowing economic output. But indications since then are that the collapse has had less economic impact than predicted.

Retail sales in November, for instance, rose 0.2 percent, a modest but still positive amount. And major retailers reported that last-minute Christmas shopping exceeded their expectations, in some cases 10 to 20 percent higher than a year before.

"I think many of the predictions {of slower economic growth} were based on assumptions that consumers would severely curtail their spending. So far we have not seen any evidence of that in any significant way," said Bretz, who is chairman of the association's survey committee.

The purchasing managers' survey found that new orders were higher than at any time since December 1983, while employment grew for the ninth time in 10 months.

The composite index, which takes into account all elements in the survey, rose to 61.6 percent in December, up from 58.9 percent in November. It was the second-highest level registered in all of 1987.

The association said index levels above 50 percent are consistent with an expanding economy, while levels below 50 percent generally occur as the economy is contracting.

The average index for 1987, 57.6 percent, is consistent with growth in real gross national product of 4.1 percent, Bretz said.