PARIS, April 17 (Reuters) - The French government's budget deficit reduction plans lack credibility in the absence of more detailed plans to reduce spending, France's independent public finance watchdog said on Wednesday.

The finance ministry said last week it expected a bigger public sector deficit in the coming years due to weaker-than-expected growth but stuck to plans to bring it in line with an EU limit of 3% of gross domestic product by 2027.

The Haut Conseil des Finances Publiques, which is mandated by law to give an independent opinion on the government's financial planning, said that reaching the 3% target in 2027 implied an unprecedented budget tightening effort.

"The Haut Conseil considers that this forecast lacks credibility," it said.

"While such an effort on spending has never been done, its details are currently lacking and implies rigorous governance bringing all actors together... which is not the case today." (Reporting by Leigh Thomas Editing by Ingrid Melander and Sharon Singleton)