Automakers are filling the streets of Motor City with fuel-saving and low-polluting gas-electric hybrids, high-mileage diesels and even exotic hydrogen-fueled vehicles, hoping to demonstrate during the high-profile North American International Auto Show that the future is here and that they are its champions, its partisans, its owners.

Ford Motor says it will build more hybrids than announced and do it sooner than planned. General Motors says it is leaping closer to real-world hydrogen fuel-cell power. Volkswagen banged the table at the Los Angeles auto show a few days ago about the need for more diesels.

Before any of the promising alternatives makes a difference in oil consumption or air quality, prices have to come down, reliability has to be proven, consumers have to be sold, and in the case of hydrogen, cheap, safe and convenient ways have to be found to make, transport and dispense the fuel.

"Internal-combustion engines are here for the foreseeable future," says Ford's Mary Ann Wright. That's no small acknowledgment for the enthusiastic director of Ford's hybrid and hydrogen vehicle programs.

Hybrids sound like just the ticket. Here now in reasonable numbers at Ford, Toyota and Honda showrooms, you fill the tanks with gasoline and drive normally.

Not according to an analysis by the Power Information Network. PIN's Tom Libby notes: "Nearly 42% of hybrid models sold in the U.S. in the last year were in California. Hybrid prices need to drop to the point where they make economic sense for consumers. Until that time, hybrids will successfully appeal only to fringe groups, including Hollywood stars and ultra-environmentalists."

Hybrids' $20,000-something prices sound reasonable, but are $3,000-$4,000 more than consumers would pay for similar gas-power vehicles.

In contrast, improved technology probably can boost efficiency of the conventional gas engine another 25%, "for a cost of maybe $1,000, and that's a hard target to match," says David Cole, chairman of the not-for-profit Center for Automotive Research.

About 84,000 hybrids were sold in the USA last year, automakers report, and J.D. Power and Associates' powertrain expert Anthony Pratt says 220,000 probably will be sold this year. He sees that climbing to 500,000 a year in 2008, then stalling. "We don't think hybrids will appeal to the masses unless gas goes beyond $3.50 a gallon in today's dollars, and we don't think that will happen through 2011," he says.

Automakers are divided on hybrids' future.

Toyota is moving aggressively.

GM and DaimlerChrysler plan to jointly develop a hybrid system that both say they'll use widely, but not for several years.

Nissan is not interested in investing in hybrids.

The big stumbling block for hybrids is the cost issue. They require two complete drivetrains -- gas and electric -- plus complex transmissions to connect the two and sophisticated computer gear to blend their power output smoothly.

Alternative fuels:

Diesels

Capable of 20% to 40% better fuel economy than gasoline engines and accounting for about 50% of new vehicle sales in Europe, diesels are about 4% of the U.S. market. Despite improvements, diesel fuel still smells worse than gas, and diesel engines still make a little more noise and smoke a little more than gas engines do.

Now that diesel fuel is more expensive than gasoline, some savings are gone, unlike in Europe, where diesel is cheaper than heavily taxed gasoline.

"There's a hesitancy for North American consumers to buy diesels, but I think you'll see that change" as cleaner, quieter diesels hit the market, says Brian Ambrose, in charge of the automotive practice at consultant KPMG.

That begins in 2006, when tougher pollution regulations take effect. Regulations also require refiners to begin selling cleaner-burning, low-sulfur diesel fuel that year. The concentration of sulfur, poisonous to pollution-scrubbing catalytic converters, drops to 15 parts per million, vs. 500 ppm now.

Finding fuel can be a challenge.

Ford's are the Mercury Meta One and the sub-compact Ford Synus sedan. Both envision burning a mix of conventional and bio-mass diesel, made from agricultural or other wastes. Meta One is also a hybrid, teaming the clean-burning diesel with an electric motor to stretch fuel economy. It also has a sophisticated exhaust-treatment system and, Ford says, would be so clean-burning that it would qualify for partial zero-emission-vehicle credits under California's strict rules.

GM's is a two-fer, too: a diesel-electric hybrid. GM is showing off the fuel-efficient powertrain in the Opel Astra, a model sold in Europe.

An advantage of diesels is that "drivers don't have to change their lifestyles," says Volkswagen Chairman Bernd Pischetsrieder. Fueling and driving them is similar to using gasoline vehicles. VW sells several diesel models, including Jetta, the best-selling diesel in the USA.

Hydrogen

It's almost literally everywhere but a little touchy to transport and store. As a gas, its natural state, hydrogen takes up an impractical amount of space. Keeping it as a conveniently compact and energy-dense liquid, though, means chilling it to more than minus-200 degrees Fahrenheit. The alternative is storing it combined with something else -- water, for instance, is a mix of hydrogen and oxygen -- and that means using a lot of energy to separate the hydrogen when you need it.

"Mass commercialization of hydrogen is maybe 20 years off" because of the challenges, says Ford's Wright.

Hydrogen is useful as fuel in two ways:

* Passing the hydrogen through special membranes that create an electro-chemical reaction, resulting in electricity to run a car motor and emitting only water vapor out the exhaust. That's a fuel-cell system.

* Burning hydrogen directly as fuel in modified versions of the ordinary internal-combustion gas engine. That's less efficient than a fuel cell and doesn't eliminate as much pollution. But it could keep costs down by continuing to use well-known powertrains and chassis instead of converting to electric drive, as fuel cells require.

Transportation and storage costs would make hydrogen, very roughly, twice as expensive as gasoline, but fuel cells are expected to be at least twice as efficient, making hydrogen no pricier overall.

Baxley says that's the first hydrogen pump at a conventional gas station in the USA and is "a significant step in bringing hydrogen from the research phase to the reality phase."

Convenient fueling will be a major issue because it's hard to store enough hydrogen on a vehicle to go very far. GM is displaying its third-generation hydrogen vehicle here, the Sequel, which has the best range yet -- 300 miles. Some gasoline vehicles can go more than 400 miles on a tank.

California and Florida are most active. California has 13 hydrogen fueling stations and about 65 hydrogen-powered vehicles in automaker-backed demonstration fleets, says Robert Hayden, spokesman for the California Fuel Cell Partnership. Gov. Arnold Schwarzenegger hopes for 150 stations by 2010.

"We're in the same phase with hydrogen as when cellphones were expensive and large and only available in the largest urban areas."

Here are alternative-power vehicles on sale in the USA now or in the near future:

Hybrids

Toyota

* Prius sedan, on sale now.

* Lexus RX 400h SUV, to go on sale April 15.

* Highlander SUV, to go on sale in June.

Honda

* Insight two-seater, Civic sedan, Accord sedan, all on sale now.

* Midsize SUV, to go on sale in three or four years.

Ford Motor

* Escape SUV, on sale now.

* Mercury Mariner SUV, to go on sale this year.

* Mazda Tribute SUV, to go on sale within two years.

* Ford Fusion sedan, Mercury Milan sedan, both to go on sale within three years.

General Motors

* Saturn Vue SUV, Chevrolet Malibu sedan, both to go on sale next year.

* Chevrolet Tahoe and GMC Yukon SUVs, to go on sale late 2007.

Nissan

* Altima sedan, to go on sale next year.

DaimlerChrysler

* Dodge Durango SUV, to go on sale late 2007 or early 2008.

Diesels

Volkswagen

* Golf, Jetta, New Beetle and Passat sedans, Touareg SUV on sale now.

DaimlerChrysler

* Mercedes-Benz E 320 CDI sedan and Jeep Liberty SUV, both on sale now.

* Mercedes-Benz M-class SUV, to go on sale this year or next.

"We don't think hybrids will appeal to the masses unless gas goes beyond $3.50 a gallon in today's dollars, and we don't think that will happen through 2011," he says.