UPDATE 1-IMF's Lagarde says nobody wins in a trade war

* Trump has backed plans for big tariffs on steel, aluminum

* "Nobody wins" in trade war -Lagarde

* Trade war could have serious macroeconomic impact -Lagarde (Adds further comments from Lagarde, detail)

PARIS, March 7 (Reuters) - The International Monetary Fund's Managing Director Christine Lagarde said on Wednesday that nobody wins in a trade war and that the macro-economic impact of U.S. tariffs on imports would be serious if other countries respond with tariffs of their own.

"The macro-economic impact would be serious, not only if the United States took action, but especially if other countries were to retaliate, notably those who would be most affected, such as Canada, Europe, and Germany in particular," Lagarde said on French radio RTL.

On Tuesday, U.S. President Donald Trump reiterated his plan to slap big tariffs on imports of steel and aluminum, warning the European Union it would get hit with a "big tax" for not treating the United States well when it comes to trade.

"In a so-called trade war, driven by reciprocal increases of import tarifs, nobody wins, one generally finds losers on both sides," Lagarde said, adding that she hoped that Trump would not implement the tariffs threat.

"We recommend an agreement between the different parties, and talks, talks," she said.

However, she indicated that Trump might have a case for threatening to slap tariffs on some imports, saying there were a few good reasons to protest against the current situation.

"There are some countries in the world that do not necessarily respect the World Trade Organisation agreements, and which impose technology transfers. China is a case in point but it is not the only country with such practices," she said. (Reporting by Geert De Clercq and Sophie Louet Editing by Sudip Kar-Gupta)