Because Mr. Burkle’s Yucaipa funds are private, and the Clintons have refused to release their tax returns, details of Yucaipa’s investments and Mr. Clinton’s potential to profit from them are not publicly available. Last year, after Mr. Clinton published a book on philanthropy that extols the virtues of investing in renewable energy and contains a reference to Cilion, a spokesman for the former president told New York magazine that he consulted for Yucaipa on renewable energy investments but was not involved in Cilion.

On Wednesday, a spokesman for Yucaipa declined to say how much it had invested in Cilion, but said it amounted to less than 5 percent of the company’s equity  small by Yucaipa standards, but enough for it to be represented on Cilion’s board. He said Mr. Clinton did not stand to profit from Yucaipa’s investment in Cilion.

Under an agreement with Mr. Burkle in 2002, Mr. Clinton was to provide advice and find investment opportunities for several domestic and foreign funds in Yucaipa’s portfolio, and would receive a share of the profits from those funds. On a financial disclosure report that Mrs. Clinton filed as a presidential candidate last year, Mr. Clinton listed several direct investments through Yucaipa, including one in a Brazilian sugar-cane ethanol company founded by Mr. Khosla, but Cilion was not among them.

Mrs. Clinton is far from alone in proposing increased federal incentives for renewable energy  her opponent, Senator Barack Obama of Illinois, backs even greater spending on biofuels  and not all of her actions on ethanol would benefit the interests of Mr. Clinton and his associates. She has voted to preserve a tariff on Brazilian ethanol imports, which helps domestic ethanol producers but works against investors in Brazilian facilities.

In fact, Mrs. Clinton had long opposed ethanol subsidies, but in May 2006, she switched gears and introduced a bill to create a $50 billion “strategic energy fund” to expand the use of ethanol and other alternative fuels. The bill, which was reintroduced last year, would direct billions of dollars to develop cellulosic ethanol, an experimental fuel made from organic materials other than corn.

Image Former President Bill Clinton with Richard Branson in 2006. Both have been involved in efforts on alternative fuels. Credit... Ruby Washington/The New York Times

In addition to the legislation, Mrs. Clinton has spent an increasing amount of time in upstate New York, promoting the region as fertile territory for renewable energy projects. In Lockport in July 2006, she said she was working with the State University of New York College of Environmental Science and Forestry  which has offered technical assistance to Cilion and other companies in the region  to support locally produced ethanol, rather than “just relying on corn in the Midwest.”