LOS ANGELES — Imagine a car that gets more than 40 miles per gallon in everyday traffic and 50 on the highway — and it isn't an expensive hybrid, and it doesn't require special fuel.

LOS ANGELES — Imagine a car that gets more than 40 miles per gallon in everyday traffic and 50 on the highway — and it isn't an expensive hybrid, and it doesn't require special fuel.

Get ready for a new generation of cars equipped with surprisingly powerful three-cylinder engines that, according to early reviews out of Europe, have both the zip and zoom Americans expect in the four-cylinder compact sedans they buy today.

"This engine is a game-changer," Steve Cropley of Autocar magazine, a British publication, said of the three-cylinder Ford Focus that just went on sale in Europe. "You barely hear the thing start, and it idles so smoothly you'd swear it had stalled."

Better yet for power enthusiasts, "this lean upstart makes some bigger engines look puny," wrote Phil McNamara of Car, another British magazine.

Automakers are starting to test the waters for how such vehicles will sell in the U.S. market. Ford Motor Co. said it will have a three-cylinder Focus or Fiesta for sale here by the middle of next year. Mitsubishi plans to launch a compact car with a three-cylinder engine sometime in 2013.

BMW, known for its full-throttle, throaty engines, is developing a three-cylinder power plant that could show up in its U.S. offerings in three to five years. Volkswagen and Nissan also are working with three-cylinder engines, but there's no word on whether or when they will hit the U.S. market.

Automakers are proceeding cautiously because previous efforts to pack tiny engines in cars for the U.S. market mostly sputtered.

In the 1990s, Suzuki sold the Swift, and General Motors Corp. sold its version of the same vehicle under the Chevrolet Metro and Geo Metro names. While the cars' fuel economy was among the best in the industry, drivers complained that they were noisy and struggled going uphill.

The Smart Fortwo, a tiny two-seater without much power, is the only three-cylinder car still being sold in the U.S., but it's not a popular model. And because it requires premium gas, its fuel economy, at least as measured by how much money is spent on gas annually, is only slightly better than that of much larger vehicles with far stronger four-cylinder engines, such as the Honda Civic and Hyundai Elantra.

To be attractive to today's drivers, any vehicles with such small engines must be sure "not to compromise performance or fuel economy," said Rebecca Lindland, an analyst with IHS Automotive.

That's why automakers are packing more power — as measured by horsepower and torque — into these new engines.

The car companies are encouraged by how quickly Americans have downsized from larger engines to four-cylinder power plants. Almost half, or 47 percent, of the cars sold last year had four cylinders, according to auto information company Edmunds.com. That's up from 34 percent in 2007. Many small sport utilities, and even some larger ones such as the Ford Explorer, also come in four-cylinder models.

"Three cylinders shouldn't be much of a stretch," said Dave Sullivan, manager of product analysis for automotive consulting firm AutoPacific Inc.

Downsizing engines is part of an auto industry strategy to meet federal fuel economy standards that require the combined industrywide fleet to average 34.1 mpg by the 2016 model year, and a proposed 54.5 mpg by 2025.