DEARBORN, Mich. — The Ford Explorer, the hulking family hauler that helped launch the SUV boom in the early 1990s, is back. And it hopes to define a new generation of more streamlined, fuel-efficient sport utility vehicles.

Ford began a marketing campaign today for the 2011 Ford Explorer, which will be in dealerships this winter. It's an important vehicle for the automaker. Ford said the Explorer is its best-known product after the Mustang.

"Explorer is really still the backbone of the brand," Ford's marketing chief Jim Farley said recently at a gathering to introduce the Explorer to the media.

The new Explorer was completely redesigned. The most obvious difference: It's built on a car platform, not a truck one, so it sits lower to the ground and has a smoother, more fuel-efficient ride.

Ford is taking a risk with customers who expect a trucklike SUV. The new Explorer will have less towing capacity than the outgoing model — 5,000 pounds, versus 7,115 pounds — and it won't offer a V-8 engine.

"It's a good test for Ford to determine what an SUV is these days," said Aaron Bragman, an analyst with IHS Automotive.

Trends in the market suggest most buyers aren't looking for the power of traditional SUVs and would prefer a more fuel-efficient vehicle. Ford's top U.S. sales analyst George Pipas said a decade ago, 85 percent of all SUVs sold were truck-based; last year, just 23 percent were.