“There is no denying that when you get negative job numbers, realistically the economy is less strong than we had hoped it would be,” Mr. Lazear said. “The question is how quickly will it pick up. We think it will pick up  as I mentioned, we think it will pick up by the summer.”

Few private forecasters were so buoyant. Many firms had already concluded that a recession was under way. Within minutes of the new report on employment, many in the dwindling pool of optimists changed their positions.

Mr. Yardeni was hardly alone. Just one minute after the Labor Department published its report at 8:30 a.m., JPMorgan Chase reversed its stance, declaring that a recession appeared to have begun. Lehman Brothers switched its position as well.

Unemployment typically starts to rise only after a recession has started, and it keeps climbing for many months after the economy has hit bottom and begun to recover.

Paul Ashworth, an economist at Capital Economics, noted that private-sector payroll employment has now declined by an average of 47,000 a month  a decline that has been followed by a recession every time it has happened in the last 50 years. In each of those recessions, Mr. Ashworth added, the job market recovered only after monthly job losses peaked at 200,000 jobs.

Ben S. Bernanke, chairman of the Federal Reserve, had already sent clear signals in recent weeks that the central bank was ready to reduce the overnight federal funds rate when policy makers meet on March 18.

Since August, the Fed has sharply cut overnight rates five times, to 3 percent from 5.25 percent, and investors have been all but assuming that the central bank would reduce them by at least another half a percentage point, and perhaps three-quarters of a point, at the next meeting.