The changes occurred in two press releases from the Department of Energy's loan guarantee program — the same program that has been the center of controversy surrounding the failed solar company Solyndra.

Both were changed to remove the name of a company that has received negative press attention in recent days, SunPower, and replace it with the name of another company, NRG Energy .

Generally, it is not considered correct procedure to revise old press releases retroactively on the Web. More commonly, government agencies will issue a new press release with a current date explaining any changes that have occurred.

In the April case, the Department of Energy loan programs office announced in a press release on April 12 "conditional commitment" to a $1.187 billion loan guarantee to support the California Valley Solar Ranch project, which it said was "sponsored by SunPower Corporation."

But that release was later changed on one website to say the project was "sponsored by NRG Energy." The date on the release remained "April 12, 2011."

The two companies are closely linked. Just before the announcement of the loan guarantee in September, NRG completed its long-in-process acquisition from SunPower of the same California Valley Solar Ranch project that had received federal support.

But in April, that project was still owned by SunPower, not NRG.

In a second instance of retroactive press release revision, someone changed a release from September 30 that announced the finalization of the California Solar Generation project. In an early version of the September 30 press release, the government said the project was "sponsored by SunPower." That was later changed to "sponsored by NRG Energy."

In a statement, a spokesman for the Department of Energy said that the changes were made by outside contractors for the department responsible for maintaining the Loan Programs Office website.

"The only website that changed was a separately maintained loan program webpage that is managed by support services contractors," the spokesman said. "While updating the project fact sheet to reflect the changes in the ownership of the California Valley Solar Ranch project, those contractors inadvertently changed the news bulletins posted on the LPO website."

Update: On Wednesday evening, a Department of Energy spokesman said that the press releases had been returned to their original content as a result of CNBC's inquiry about the changes.

Correction: A previous headline on this article incorrectly characterized the press releases as being related to Solyndra.