Chicago ? A flourishing defense business helped Boeing Co. post a $590 million profit in the fourth quarter despite the aviation industry slump that inflicted a $3 billion hit on sales at its mainstay unit, commercial airplanes.

Facing another tough year ahead, however, the aerospace giant lowered its revenue estimate for 2003 by another $1 billion and cautioned that full-year earnings could fall short of Wall Street’s expectations.

Net earnings amounted to 73 cents a share, compared with $100 million, or 12 cents a share, a year earlier.

But excluding nonrecurring items such as Sept. 11-related charges in the fourth quarter of 2001, earnings were down 21 percent to $571 million from $722 million a year earlier. Per-share earnings of 71 cents met the consensus estimate of analysts surveyed by Thomson First Call. Revenue was $13.7 billion, down from $15.7 billion.

Boeing is Kansas’ largest private employer with 12,000 workers.