UPDATE 1-German nuclear commission chief warns utilities against delaying provision deal

* Co-chair warns utilities against prevaricating

* Commission was expected to finalise deal in mid-April

* Further date for talks set for April 21 - source (Adds new date for talks, context)

FRANKFURT/BERLIN, April 7 (Reuters) - Delaying a deal to secure the funds needed to pay for closing down Germany’s nuclear power plants would be the “worst case” for the country’s utilities, the co-chairman of a commission tasked with finding the solution said.

Germany’s last nuclear plant is due to be shut down by 2022 and it is feared the 39 billion euros ($43 billion) so far set aside in provisions by the big four utilities will not be enough to cover the costs.

A government-appointed commission chaired by Green ex-environment minister Juergen Trittin is trying to decide how to apportion the costs for the decommissioning of plants and the storage of nuclear waste.

The commission was originally scheduled to present proposals on how to secure the funding by the end of February, but the complexity of the task has delayed talks.

The last date to settle talks had been set for April 13. In a sign of the potential challenges still ahead, the commission has suggested a further meeting on April 21, a source close to the talks told Reuters on Thursday.

“If we don’t start working on a law this year I don’t expect we’ll get another chance before 2018 or 2019,” Trittin said at an event in Berlin on Wednesday.

“All analysts agree that this would be the worst case with regard to the companies.”

A solution is expected to see the utilities - E.ON , RWE, EnBW and Vattenfall - paying existing provisions made for the interim and final storage of nuclear waste into a government-controlled fund.

But there is still uncertainty on various issues, including whether additional payments will need to be made to release the utilities from further liabilities on the storage costs.

“Bargaining positions are still far apart,” Trittin said.

Investors and analysts have pointed to the unresolved conflict over provisions as the main concern with regard to the utilities.

$1 = 0.8775 euros Reporting by Christoph Steitz and Caroline Copley; Editing by Greg Mahlich and Mark Potter