Last spring, Doerr and the Greentech Innovation Network, a group of academics, entrepreneurs, and business leaders (including at least one from Wal-Mart) organized by Kleiner Perkins, lobbied hard in Sacramento to limit greenhouse gases. Governor Arnold Schwarzenegger signed the bill with enthusiasm, sending shock waves through the corporate world. Suddenly business leaders began talking about nationwide carbon caps, to avoid a state-by-state patchwork of regulations. Carbon caps, of course, would boost the market for alternative energy.

Doerr and fellow Valley activists went largely undefeated until last fall, when a ballot proposal to tax oil drilled in California and fund alternative-energy research failed. Supporters pumped more than $50 million into a P.R. blitz but were no match for the old-school energy industry, which ­counterattacked with nearly $100 million.

Technet moved its headquarters from Palo Alto to the nation’s capital in 2005. It also hired Karl Rove’s former deputy, a schmoozer named ­Lezlee Westine, as C.E.O.  As Mr. Doerr goes to Washington, however, he is headed for the same buzz saw he ran into in California. “When you get into energy, you’re going up against Exxon and Chevron and cattlemen and corn. This is not a niche play,” says former Democratic operative and current lobbyist Tony Podesta.

Simon Rosenberg, whose NDN (formerly the New Democrat Network) has received Doerr donations, says, “This man has put money, time, and sweat into public policy the way no one in Silicon Valley has.” Yet, he says, the tech lobby has been tarnished by the dotcom bubble, the outsourcing of jobs overseas, and a weak record on job creation for average Americans: “They’re not the special children they were in the 1990s.”

Doerr has an unlikely solution to the tech-bubble problem: He denies there ever was one. “People think of it as a bubble,” he says, gesticulating enthusiastically. “I prefer to think of it as a boom. The payoff on some of these innovations was longer term.”

Already, alternative energy has mushroomed into one of venture capital’s fastest-growing categories. Last year alone, V.C. firms in the U.S. and Canada poured $2.1 billion into alternative energy, according to estimates from the Cleantech Venture Network, a jump of 290 percent in the past two years.

Asked if greentech could repeat the dotcom crash, Doerr admits, “It’s possible.” He pauses and rubs his forehead before repeating, “It’s possible.”

Kleiner Perkins partner Ray Lane, a sage 60-year-old, goes further. “A bubble? You can almost count on it,” he says. “Bubbles are common. They end badly for those who come in late. For those who come in early, it’s not that bad.” Lane thinks Kleiner Perkins’ greentech portfolio has big, long-term winners in it. But he predicts that alternative energy will get overheated and others will undoubtedly go up in flames. “If the bubble develops out of a whim,’’ he says, “then shame on investors. They need to get burned.”