ROME, Nov 25 (Reuters) - Italy's government will fight a judicial appeal by the city of Piombino against a key plan to install a new liquefied natural gas (LNG) floating terminal in its port, the country's energy and environment minister said on Friday.

The Tuscan coast city has turned to an administrative court to stop the LNG terminal project, which the government sees as key to helping wean Italy off Russian gas in the wake of Moscow's war on Ukraine.

"We certainly need those 4-5 billion cubic metres (annually) that would come from Piombino," Minister Gilberto Pichetto Fratin said on the sidelines of an event in Rome.

The special commissioner for the project, Tuscany president Eugenio Giani, said on Friday he planned to have a role in the legal case to defend its decision to give the project the go-ahead.

A spokesperson for Italian gas grid operator Snam , which has bought the LNG vessel and is working on connecting it to the national gas grid, said the company was assessing the arguments of the challenge and would prepare a memo on the matter.

The dispute pits Piombino mayor Francesco Ferrari, who is from the Brothers of Italy party, against a national coalition government led by his own party.

In its legal challenge, the city of Piombino argues that the floating storage and regasification unit (FSRU), the Golar Tundra vessel, would be structurally unfit to operate safely in the port, advisers for the city told Reuters.

They added that the only way to allow the vessel to operate without blocking ordinary traffic in one part of the port would be to dredge the seabed for "hundreds of thousands of cubic metres", which would take years.

This would make it impossible to have the terminal operational by the end of March next year, as planned, the advisers added. (Reporting by Angelo Amante and Silvia Ognibene and Giulio Piovaccari, editing by Alvise Armellini, Keith Weir and Louise Heavens)