Given all the hype about green jobs—particularly the rosy projections about the green jobs of tomorrow—it’s welcome news when a credible source puts some facts on the table.

Would you care to guess how many green jobs there are in America?

No one can be sure, but a careful and comprehensive survey just released by the Pew Charitable Trusts turned up 770,000 of them, as of the end of 2007.

That’s a good number of jobs and they are spread across all 50 states, according to Pew.

But it’s a long way from there to 5 million, a number often tossed around by politicians and environmentalists who want to persuade voters that dealing with the threat of climate change is good way to create jobs.

Particularly in this downturn, environmental groups and politicians love to talk up green jobs. Environmental Defense has run commercials about green jobs. The American Council for an Energy-Efficient Economy issued a news release this week saying that the energy-efficiency provisions of Waxman-Markey would  by themselves, create “approximately 250,000 jobs…by 2020, with a total of 650,000 jobs generated by 2030.” President Obama said last year that spending $150 billion on the clean energy economy could create 5 million jobs.

By contrast, the Pew Report is restrained. It does not project the future. It does not attempt to link particular government policies with the growth of green jobs. It measured the growth of green jobs, but one of its authors admitted that no attempt was made to see if any of those jobs replaced others that disappeared. (Creating 1,000 new jobs to make homes more efficient might mean less work for the truck drivers who make deliveries of home heating oil.) Pew lays out a limited and relatively conservative definition of green jobs. People making wind turbines and solar panels are doing green jobs, as are handymen doing weatherization of homes. Farmers growing corn for ethanol are not. An arbitrary line, perhaps, but there it is.

The encouraging news from Pew is that the “clean energy economy” has for a decade or so been producing jobs faster than the rest of the American economy. Pew found that jobs in the clean energy economy grew at a national rate of 9.1 percent, while traditional jobs grew by only 3.7 percent between 1998 and 2007.

Pew also sought to put the “clean energy economy” into context:

America’s clean energy economy has grown despite a lack of sustained government support in the past decade. By 2007, more than 68,200 businesses across all 50 states and the District of Columbia accounted for about 770,000 jobs.

By comparison, the well-established fossil-fuel sector—including utilities, coal mining and oil and gas extraction, industries that have received significant government investment—comprised about 1.27 million workers in 2007.

Pew  produced state-by-state accounts of green jobs, a great way to publicize the issue in local media, and so lots of reporters called in to a telephone news conference announcing the results.

“It isn’t just California,” Pew’s Lori Grange said. “Every state has a piece of the clean energy economy….Trends point to explosive growth in this sector.” States like Ohio, Texas and Pennsylvania all added significant numbers of green jobs during the decade, she noted.

Buttressing that view was venture capitalist David Prend of Rockport Capital. “I believe we’re just in the first inning of this growth,” he said. “Clean technology is where infotech was 30 years ago and biotech was, maybe, 20 years ago.”

Let’s hope he’s right. I’d love to see clean technology grow and create millions of jobs. The question is, what’s the best way to spur that growth? And how deeply should the government be involved? Those questions are outside the purview of the Pew report.

Don’t forget: It’s relatively easy for the government to help spur the creation of new jobs. It can spend money on any number of things—schools, day care centers, social services for the elderly, roads, police, fighting in Iraq and Afghanistan. Jobs will follow. It can rescue GM or Chrysler, as it has, and save jobs, at least for now.

But it’s my view that questions about government policy are best examined on their own merits—and not through the narrow prism of “jobs.”

If it’s important for governments to deal with the threat of climate change—and of course it is—then the government should do what it needs to do.

If passing a cap-and-trade scheme, or subsidizing solar power, or setting efficiency standards for appliances will also help create new jobs, terrific. But if they don’t, they may be worth doing anyway.