(Updates with minister's replacement)

PARIS, Feb 22 (Reuters) - French Environment Minister Nathalie Kosciusko-Morizet said on Wednesday she was leaving the cabinet to become a spokeswoman for President Nicolas Sarkozy in a job switch designed to boost his flagging popularity before presidential elections.

Kosciusko-Morizet, 38, who is often referred to by her initials NKM and known for her sense of understated chic, is seen as a feminine counterpoint to Sarkozy's perceived brashness ahead of the April-May election.

She is becoming Sarkozy's campaign spokeswoman at a time when opinion polls show he would lose the election to Francois Hollande, his Socialist rival, and while he is struggling to reconnect with voters anxious about issues such as unemployment and immigration.

"This is my last cabinet meeting because I will present my resignation tomorrow," Kosciusko-Morizet told reporters after a meeting between ministers and Sarkozy at the Elysee palace.

Kosciusko-Morizet is a former MP, a supporter of green issues, and was reported to be close to Jacques Chirac, Sarkozy's predecessor as the head of the ruling centre-right UMP party. She has been environment minister since November 2010.

Her duties at the Environment Ministry will be taken over by Prime Minister Francois Fillon, Transport Minister Thierry Mariani and a junior minister.

One of her final acts as environment minister was to ask the European Commission on Monday to suspend its decision to allow Monsanto to plant its genetically modified MON810 corn.

She said she was resigning to avoid any appearance of conflict of interest .

Although recent opinion polls suggest Sarkozy is staging a fight back, he faces an uphill battle to win a second term. On the left he is trailing Hollande, while on the far-right Marine Le Pen, the leader of the National Front, is cashing in on popular unease about immigration controls. (Reporting by Emmanuel Jarry; Writing By Alexandria Sage, editing by Andrew Osborn)