During a visit to a General Motors transmission plant in White Marsh last week, Hillary Clinton pitched a plan that would invest billions in clean energy research and infrastructure improvements that would create 5 million green-collar jobs over the next 10 years. "This is the equivalent of the space race," she told workers. Not to be outdone, Barack Obama offered an almost identical plan later in the week to autoworkers in Wisconsin.

Green is the color of the current political season and perhaps the future, a way to boost the economy while beating global warming. It sounds great, New Wave-ish and ecologically correct, but the rhetoric offered so far leaves lots of unanswered questions.

Building a green-collar economy would be a massive undertaking, demanding a significant reshaping of the U.S. economy - an endeavor that would require more than just government spending. There is a real danger that many of the billions invested in government green-collar development might turn into pork-barrel spending, offering relatively few improvements in energy efficiency and fewer permanent jobs. In the 1990s, the Clinton administration spent many millions on a joint venture by the big three automakers to produce a superefficient 55 miles-per-gallon car. The partnership was likened to the Apollo project, but the car never arrived.

Still, the green jobs program has appeal. Many of the jobs in energy infrastructure improvements would be intensely local - in or near older, economically troubled urban areas. New biomass energy sources could boost depressed rural economies. Also, if real gains are made in producing cleaner fuels, more efficient cars and consumer goods, these improvements could produce significant economic pluses for American businesses and workers in the world economy.

Success would depend on convincing millions of ordinary Americans that going green makes economic sense for them and in finding ways to let markets, not bureaucrats, promote the green evolution. These are the same Americans who insist on gas-guzzler SUVs, resist buying light bulbs that would reduce home energy consumption and protest the erection of windmills and solar panels where they might ruin the view.

But kick-starting the greening of America's economy should be pursued because oil isn't getting any cheaper and the planet isn't getting any cooler. And if it inconveniences some of us, keep in mind that our grandchildren will be grateful.