The U.S. economy slowed to a crawl in the fourth quarter of the year, growing at just a 0.7 percent annual rate, the Commerce Department estimated Thursday. For all of 2002, the economy grew a respectable 2.4 percent. Much of the growth in 2002 was due to defense spending, inventory restocking and unsustainable growth in homebuilding and auto sales. Business spending fell at the highest rate in 27 years. For the fourth quarter, defense spending provided the biggest boost to growth. Consumer spending rose 1 percent, as auto sales fell. Business investment rose for the first time in nine quarters in the fourth quarter.