The nation’s manufacturing firms were growing at a very strong pace in January, according to a closely followed survey of top executives released today, MarketWatch reported.

The Institute for Supply Management (ISM) index rose to 58.4 percent from 54.9 percent in December, above the 56 percent expected by economists surveyed by MarketWatch.

It’s the index’s highest reading since August 2004.

Readings over 50 percent in the ISM diffusion index indicate that more firms are growing than contracting. The ISM tracks the breadth of growth across firms, asking purchasing managers if business is better this month than last.

Both new-orders and production indexes rose above 60 percent.

Thirteen of 18 industries as tracked by Tempe, Ariz.-based ISM were growing in January, up from nine in December.

“This month’s report provides significant assurance that the manufacturing sector is in recovery,” said Norbert Ore, head of the ISM’s survey committee.

“It appears that it is sustainable,” he added.

After worrying that the recovery would be tepid, Ore said he has now changed his mind. “This looks like a typical recovery, where we see strong growth in the front of it,” he said.

Contacts report that conditions “are improving significantly,” Ore told reporters at a briefing.

January’s new-orders index rose to 65.9 percent from 64.8 percent in December, the ISM’s data showed.

The production index increased in January to 66.2 percent from 59.7 percent.

The employment index increased to 53.3 percent from 50.2 percent in the prior month. The prices-paid index rose to 70 percent from 61.5 percent.

The inventories index rose to 46.5 percent for January, December’s reading was 43 percent.

New export orders were very strong again in January, rising to 58.5 from 54.5 in December.