WASHINGTON (Reuters) - U.S. wholesale inventories rose in line with expectations in September, reinforcing the view that much of the strength in economic growth during the third quarter came from businesses restocking their shelves.

The Commerce Department said on Friday wholesale inventories rose 0.4 percent in September, matching the median forecast in a Reuters poll of analysts.

Gross domestic product expanded at a 2.8 percent annual pace in the July-September period, though nearly a third of that growth came from inventory building. Most analysts expect a significant slowdown in the fourth quarter and for businesses unwind some of that restocking.

A government shutdown that left hundreds of thousands of people out of work for weeks in October is expected to also dent fourth quarter growth.

Wholesale inventories in September were boosted by a sharp increase in stocks of professional equipment and computers, while dealers reduced stocks of autos in their dealerships.

Sales at wholesalers increased 0.6 percent, beating economists' expectations.

At September's sales pace it would take 1.18 months to clearshelves. The inventories/sales ratio was unchanged from August. (Reporting by Jason Lange; Editing by Krista Hughes)