ORION TOWNSHIP, Mich. — The only subcompact car being built on American soil will soon roll out of an assembly plant here in suburban Detroit that is as unusual as the car itself.

The production line has been squeezed into half the space of a traditional plant. Welding robots are concentrated in efficient clusters, instead of being spaced along the line, while many of the workers earn half the typical union wage. Even the first coat of rust-proofing has been reformulated so that it is one-hundredth as thick as — and thereby cheaper than — the coating on other cars.

One of the oldest axioms in the auto industry is that no company can build a subcompact car in the United States and make money because they are priced too low. The Ford Fiesta is built in Mexico. The Honda Fit is made in several places, including China and Brazil. But with Americans — and Detroit — rediscovering small cars because of high gasoline prices, General Motors is intent on shattering that notion with its new Chevrolet Sonic. The car, with a base price of around $14,000, will give G.M. a new entry in the lowest tier of the market when it goes on sale this fall. The Sonic is also expected to be a breakthrough in establishing a new level of cooperation between Detroit and the United Automobile Workers.

The radically revamped factory here operates with fewer and cheaper workers, many of whom are paid $14 an hour rather than the full U.A.W. wage of $28 an hour.