NEW YORK – Manufacturers, already hit by mounting job losses, saw business plummet to the lowest level in 26 years in October. Sharply lower auto sales and shrinking construction spending, meanwhile, provided more evidence the U.S. has entered a recession that may be deep and prolonged.

The Institute for Supply Management said earlier this week that its manufacturing index fell to 38.9, the lowest reading since September 1982, when the country was near the end of a 16-month recession. Any reading below 50 signals contraction.

In separate reports, automakers said their sales fell in October in what may be the worst drop in 25 years.

Sales sank 45 percent at General Motors Corp., 30 percent at Ford Motor Co., 25 percent at Honda Motor Co. and 23 percent at Toyota Motor Corp.

“Everything we can tell about the economy just got weaker,” said Stuart G. Hoffman, senior vice president and economist for The PNC Financial Services Group. The manufacturing report confirmed the economy is falling deeper into recession, Hoffman said.

The manufacturing index had been hovering near what economists call “the boom-bust” line for most of the year until its sharp fall in September brought it to the lowest level since the aftermath of the Sept. 11 attacks.

October’s reading of 38.9 was sharply below the September figure of 43.5 and lower than economists’ expectations of 41.5, according to the consensus estimate of Wall Street economists surveyed by Thomson/IFR.

Manufacturers, already hurting from declines in construction and consumer spending, were further battered by the credit crisis and gulf coast hurricanes.

The overall unemployment rate was 6.1 percent in September for the second straight month, the highest it’s been in five years.