With fuel prices nearing record levels in the U.S. , and little relief in sight, American motorists must consider the seemingly unthinkable. Yet in a nation that might easily emblazon the mantra, "bigger is better," on its flag, the idea of downsizing seems downright unpatriotic.

While hybrid vehicles are touted as a solution, the practical reality is that they work for only some motorists, and only in select driving conditions. So what are drivers of full-size pickups, seven-passenger SUVs, and 500-horsepower musclecars to do?

Volkswagen thinks it has the answer in the form of a steadily expanding lineup of diesel-powered vehicles, including the Golf, Jetta, and GTI. Demand has been so strong VW dealers can barely keep up, even though overall sales are sluggish, at best.

Ironically, while there are signs Americans are ready to rediscover the diesel, tough new emissions standards threaten to drive the technology out of the U.S. entirely.

In the wake of the 1979 Iranian oil crisis, Americans embraced the high-mileage powertrains. Well over half of all Mercedes-Benz products were diesels in the early 1980s, and other manufacturers rushed offerings of their own - a big part of the problem.

It was bad enough that '80s-era diesels were slow, smelly, and rough. It made matters only worse when a highly touted engine developed by General Motors' Oldsmobile division began to fail catastrophically, and in large numbers. As memories of the fuel shock faded, American drivers quickly returned to their beloved gas engines.

There are some exceptions; Volkswagen, for example, and DaimlerChrysler's Dodge division has done well with the relatively old-style diesel offered in its big Ram pickup. Mercedes revived its E-Class diesel last year. But most manufacturers, even those with the most advanced diesel technology, are reluctant to bring it to the States.

There are several reasons why, cautions Audi's chief U.S. executive, Johan de Nysschen. For one thing, tough new federal emissions standards are coming, and smoggy California has set even tougher rules which, under federal waiver, have been adopted by a number of other states collectively accounting for a quarter of the American car-buying population. Makers like Audi, acknowledges de Nysschen, don't want to invest in a costly technology that would be off-limits in much of the country.

On the other hand, rules are about to go into effect mandating a new generation of clean diesel fuel, notes Jens Mueller-Belau, the technical manager for the giant Dutch oil company, Shell. Currently, U.S. diesel fuel contains up to 500 parts per million of sulfur. By the end of the year, that drops to 15 ppm in about 90 percent of the diesel fuel sold in America.

"This is the enabler of future diesel technology - like you see in Europe - particularly the after-treatment systems which are critically dependent on ultra-low sulfur," explains Mueller-Belau.

The problem is not entirely solved, however. The new California emissions rules are far stricter than even the latest European standards, requiring still newer control systems. DaimlerChrysler CEO Dieter Zetsche insists the new Mercedes BlueTec concept, which uses a urea after-treatment, will comply, and he has promised to introduce it, probably sometime in 2007, as the first so-called "50-state" diesel.

Audi and Volkswagen believe they will soon be ready with comparable technology, though they're being a bit coy about launch timing. An Audi insider confided that the new Q7 sport-utility vehicle might be the first model to get a diesel in the States.

Indeed, the manufacturers who could use the high-mileage technology most market the biggest, fuel-thirstiest vehicles, asserts analyst Dan Gorrell, of California-based Strategic Vision. Chrysler is cautiously moving in the diesel direction, and U.S. chief executive Tom LaSorda hints more are under development - likely sharing Mercedes' BlueTec system.

General Motors and Ford, however, are playing things cautiously. Mark Fields, Ford's President of the Americas , reveals a diesel is under development for the big F-Series pickup since, "on the truck side of the business, there's less resistance from consumers." But memories run deep, and U.S. passenger car buyers still recall the ancient diesels of the '80s, he argues, adding it will take time for them to discover the smooth, quiet, and clean modern diesel.

Compounding the problem, there aren't many diesel pumps in the U.S. right now, most found at big truck stops. But Shell's Mueller-Belau says that would change fast if demand grows.

Perhaps the biggest motivator, according to Fields, would be a shift in tax policy. Two decades ago, many states reduced taxes on diesel, and as in Europe today, lower costs spurred demand. President George W. Bush has raised a similar prospect, and legislators might even extend the current hybrid tax incentives to diesel vehicles.

For the moment, there are numerous obstacles to a U.S. diesel revival. But with new technology and government support, that could change in the next few years.