In one project, which Dr. Brilliant brought with him to the job, Google.org will try to develop a system to detect disease outbreaks early.

Dr. Brilliant likens the traditional structure of corporate foundations to a musician confined to playing only the high register on a piano. “Google.org can play on the entire keyboard,” Dr. Brilliant said in an interview. “It can start companies, build industries, pay consultants, lobby, give money to individuals and make a profit.”

While declining to comment on the car project specifically, Dr. Brilliant said he would hope to see such ventures make a profit. “But if they didn’t, we wouldn’t care,” he said. “We’re not doing it for the profit. And if we didn’t get our capital back, so what? The emphasis is on social returns, not economic returns.”

Development of ultra-high-mileage cars is under way at a number of companies, from Toyota to tiny start-ups. Making an engine that uses E85 — a mixture of 85 percent ethanol and 15 percent gasoline — is not difficult, but the lack of availability of the fuel presents a challenge, said Brett Smith, a senior industry analyst at the Center for Automotive Research in Ann Arbor, Mich.

Another barrier, Mr. Smith said, lies in the batteries for so-called plug-in hybrids, which require more powerful batteries that charge more quickly than the current generation of hybrid batteries.

There are skeptics, too, among tax lawyers and other pragmatists familiar with the world of philanthropy. They wonder whether Google’s directors might be tempted to take back some of the largess in an economic downturn.

“The money is at the beck and call of the board of directors and shareholders,” said Marcus S. Owens, a tax lawyer in Washington who spent a decade as director of the exempt organizations division of the Internal Revenue Service. “It’s possible the shareholders of Google might someday object, especially if we go into an economic depression and that money is needed to shore up the company.”