The U.S. trade deficit shrank by 5.4 percent from July through September, the third consecutive quarterly decline, the Commerce Department said Monday. The imbalance between imports and exports narrowed to $28.5 billion, the lowest quarterly deficit since the first quarter of 1985. The decline followed a revised 14.3 percent narrowing in the second quarter, when it shrank to $30.15 billion. In the first three months of the year, the deficit had fallen by 14.6 percent. For the first nine months of this year, the trade deficit has been running at an annual rate of $125.2 billion, down 22 percent from the record deficit of $160.3 billion in 1987. Economists believe this trend will hold for the final three months of the year.