DETROIT  The Chevrolet Volt, a plug-in hybrid, will not arrive in showrooms until late 2010. But it is already straining under the weight of an entire company.

Executives at General Motors, the largest and apparently the most imperiled of the three American car companies, are using the Volt as the centerpiece of their case to a skeptical Congress that their business plan for a turnaround is strong, and that a federal bailout would be a good investment in G.M.’s future.

In ads that ran this week, the company said of the Volt: “This is not just a car. It’s a vision of our future.” Another claimed that the vehicle would “completely reinvent the automotive industry.”

There is a long tradition in Detroit of relying on a single new model or technology as a silver bullet to quickly solve bigger problems. Sometimes it works  the Chevrolet Corvette, the Ford Mustang and Ford Taurus, and Chrysler’s K-car lineup of compact, fuel-efficient cars in the early 1980s all gave their companies an enormous boost.