I say yes, but predominantly in the stages where private companies consider it "too risky" to do it themselves. Classic example is the space program (which is still risky, but at least there are privately funded entrants in the market, thus justifying *continued* government "investment and management" in it), but in the area of "power systems" I think both taking the electrical grid to the next generation of technology as well as "better, less polluting nukes" both qualify. There are other technologies that private ventures are active in *managing* but can't find the investment resources that deserve government funding, like batteries, new solar conversion tech, and waste recycling tech (some of which produces energy....).
The primary fallacy I'd like to slay on this topic is the notion that private investors will always invest if there's a real potential for returns. The fact of the matter is, even in the "high-risk" Venture Capital community, there is actually a huge aversion to risk. If you've got a startup, I can guarantee that the most likely response you will get from VCs in the early rounds is a variation of "if you can get 2 other VCs to say yes, then I'm interested." (Unfortunately, when they all say that, you still have no funds!).
Government has a very important role in moving very early stage R&D forward: No, this is not advocating that "incompetent government run everything," just that people with money are often to scared and too stupid to see when there's something that's really important out there that's useful, and government money *accelerates* achievement of these capabilities. It can often also create a level-playing field with non-proprietary discoveries that can by pass nasty "standards wars" by resolving them early.
I am hoping that the era of Reagan's "the government is the problem" is finally over...without government investment in Green Tech, American VC's are going to cooperate with more forward looking foreign governments to ensure that the rest of the world leads....
Most people get interested in stocks when everyone else is. The time to get interested is when no one else is. You can't buy what is popular and do well,

Buffy