A steep decline in the stock price of General Growth Properties Inc. prompted a top executive of the company to sell half of his common shares this week to cover a margin call.

Bob Michaels, General Growth's president and chief operating officer, sold 700,000 shares Tuesday at an average price of $27.13, according to a filing with the Securities and Exchange Commission.

The sale left Mr. Michaels with 690,507 common shares in General Growth, which develops and owns shopping malls.

Mr. Michaels, who joined the Chicago-based company in 1972, serves on the board in addition to his executive post. General Growth owns more than 200 U.S. malls.

General Growth's stock has fallen nearly 50% from its year-ago level primarily because of investors' concerns about the weakening U.S. retail environment and General Growth's $18.4 billion in debt coming due in the next 3½ years.