WASHINGTON — Some White House officials were so concerned last year about the financial health of Solyndra, a solar equipment manufacturer that had received federal loans, that they warned that a presidential trip to the company’s California factory could prove a major embarrassment, newly disclosed e-mails show.

The e-mails, gathered as part of a Congressional investigation into the Department of Energy loan program, offer new insight into just how worried administration officials were about the $528 million loan to Solyndra, which is now in bankruptcy, as well as other government efforts, amounting to $16 billion in loan guarantees, to promote clean energy. The warnings came from both inside the White House — an official in the Office of Management and Budget wrote that the visit could be “embarrassing in the not too distant future” — as well as from private investors, including one Democratic campaign contributor who wrote to the White House the day before the president’s May 2010 visit to Solyndra to urge officials to reconsider the trip.

“I just want to help protect the president from anything that could result in negative or unfair press,” Steve Westly, a California venture capitalist and an Obama contributor, wrote in May 2010 to Valerie Jarrett, a senior adviser to the president. “If it’s too late to change/postpone the meeting, the president should be careful about unrealistic/optimistic forecasts that could haunt him in the next 18 months if Solyndra hits the wall, files for bankruptcy, etc.”

The Solyndra loan, which was completed in September 2009 and could cost taxpayers a half-billion dollars, has come under Congressional scrutiny since the company declared bankruptcy last month. The business is also under investigation for possible fraud by the Federal Bureau of Investigation.