* Flow of state aid to GM cannot be fully prevented -EconMin
* Contracts could give creditors security -EconMin
* Opel needs 1.9 billion euros funds from GM -EconMin
(Adds detail, background)
FRANKFURT, March 16 (Reuters) - Opel's hopes of getting state aid were dealt a blow on Monday when a German government enquiry found it was not possible to completely separate the troubled carmaker from its U.S. parent General Motors (GM.N).
Germany is open to the possibility of helping Opel but has said it needed to be sure no state support would find its way to GM. Opel has said it needs financial support to survive.
The economy ministry's findings, presented to the economic committee in German parliament, gave some hope hope, saying: "It could be attempted to give German creditors or guarantors a certain security through contracts".
GM Europe submitted a rescue plan for Opel last month under which its German unit and Britain-based Vauxhall unit would be partly spun off into a new subsidiary. It said the independent unit would need 3.3 billion euros ($4.3 billion) in state aid.
Germany has said it would make state aid for Opel dependent on whether that support would help rescue the carmaker and put aid to work where it was needed.
According to the ministry paper on Monday, the rescue plan foresees cutting Opel's production capacity by around 25 percent, which could involve closing three production sites.
"But there are no concrete decisions yet," it said, adding there were ongoing talks with the company's works council.
Support needed from parent company GM totalled 1.9 billion euros, the ministry said. It said the 3.3 billion euro figure GM Europe had mentioned in its rescue plan had included funds transferred late in 2008 and in the first few weeks of 2009. (Reporting by Maria Sheahan; Editing by Dan Lalor) ($1 = 0.7737 euro)