Mar. 1--The downturn in the auto industry has spread to just about every company that makes parts and materials that go into cars. That includes rubber, plastic and, of course, steel.

And few steel-processing companies have been socked as hard as Worthington Industries, which is a supplier to Detroit's Big Three.

Worthington had the worst quarter in its history for the three months that ended in November, with a massive inventory write-down and the announced closing of several plants.

Chief Executive John P. McConnell is trying to steer Worthington out of the downturn, the most challenging time in his 16 years at the helm.

"We have to prepare ourselves for something that will worsen," he said in a recent interview.

McConnell, 55, expects his industry to be even more competitive after the recession, with fewer but stronger players to emerge.

Worthington is larger and more diversified than many other auto-industry suppliers, so it's positioned to weather a downturn better than some of its peers. These days, the problem is that the auto-industry slump is happening at the same time as a slowdown for commercial builders, the company's other main client.

About 25 percent of Worthington's sales are to the auto industry, split about evenly between the automakers themselves and parts suppliers. The company's products include the steel for body parts and smaller items such as tracks for vehicle seats and the metal portions of seat-belt latches.

"Most parts-makers are tied up with one or more of the Big Three," said James Rubenstein, a Miami University professor who writes about the auto industry. "What we don't know is if they can replace that business."

Steel prices have plummeted, which hurts companies such as Worthington that bought supplies when costs were higher.

Low prices also indicate a lack of demand for steel, which usually coincides with a lack of demand for steel processing.

Prices bottomed out in November and then showed signs of gradual growth. Yet, an analyst warned early last week that prices are likely to fall again because of overabundant supplies from China.

"The danger is that without an increase in end-user purchasing, prices will fall and traders will refuse to take stock from the mills," said Andrew Snowdowne, writing for UBS Investment Research. His comments, in a research note about global-steel conglomerate ArcelorMittal, helped push corporate share prices lower across the steel industry, including for Worthington.

Worthington has had a rough few months.