WASHINGTON — Republicans investigating the government’s investment in a bankrupt solar panel manufacturer have concluded that the Obama administration ignored numerous red flags about the company’s financial viability, leaving taxpayers on the hook for more than $500 million.

For months, Republican lawmakers have made the government’s loan to California-based Solyndra Inc. the centerpiece of their criticisms of President Obama’s $787 billion economic stimulus package. The release of the report Thursday by the House Energy and Commerce Committee gave them another opportunity to reinforce that message.

The White House countered that the report showed that none of the accusations that Republicans had made about political interference in approving the loan turned out to be true. Democrats on the committee also released a memorandum taking issue with the findings.

‘‘The Republican report is partisan and one-sided. It does not substantiate the primary allegation that motivated the committee’s Solyndra investigation, which is that the loan guarantee decision was a form of political payoff to a campaign contributor,’’ the Democratic memo said.

The Energy and Commerce investigation lasted 18 months and included the review of more than 300,000 pages of documents. Backers of the loan have said competition from Chinese solar panel manufacturers was a major factor in Solyndra’s failure. The report said White House Office of Management and Budget staff was aware that China’s effort to penetrate the US market could hurt Solyndra.

An e-mail from an OMB reviewer in August 2009 said pricing pressures from China ‘‘raise concerns about how strong Solyndra’s position will be in the face of rising competition.’’ The reviewer had requested to his supervisor that the Solyndra loan be postponed, the report said.

The panel said federal workers also identified risks when the Energy Department and OMB reviewed a restructuring of the loan in late 2010 and early 2011, but the agencies allowed it to move forward. Solyndra filed for bankruptcy protection in September 2011.