On top of worries about the Persian Gulf, falling real estate values and slow consumer spending, the big imponderable is the job market. If employment remains strong, the economy may sputter, but it won't slide into reverse. Unfortunately, judging by recent surveys of consumer confidence, a sizable percentage of Americans fear their paychecks are in jeopardy. That has sparked a parsimonious attitude toward spending. Last week, Federal Reserve Chairman Alan Greenspan warned that shrinking employment and a decline in the number of hours worked has caused personal income to shrink. "This drop in real purchasing power, along with plunging consumer sentiment, does not bode well for the near-term trends in consumer demand," he said. A further test of the job market comes Friday, with the report on unemployment for November.