By Dominique Vidalon and Elizabeth Pineau
PARIS (Reuters) - France on Sunday renews half of its senators' seats, in a vote that is important for President Emmanuel Macron's reform plans and will be a test of his declining popularity, just four months after his election in May.
Macron's Republic on the Move (LREM) is not expected to win majority, both because of the electoral system -- only mayors and regional councilors elected before 17-month old LREM even existed vote, not the general public -- and because Macron has plans that are unpopular with many local councilors.
What is at stake instead, is whether LREM and allies will win enough seats to give Macron a three-fifths majority vote in both houses of parliament, which he needs for constitutional reforms, including plans to overhaul parliament.
There are 171 out of 348 senate seats up for renewal and the three fifth majority question may not be immediately clear on Sunday as it might require talks with other groups, including some senators who would break away from The Republicans' conservative party to create their own faction, as they did in the lower house of parliament.
The election comes as Macron's approval ratings have dropped considerably in opinion polls, dragged down by labour reforms and planned budget cuts, including a decrease in housing aid for students.
Besides, a number of local officials are unhappy with Macron's plans to cut subsidies to local authorities.
LREM currently has 29 senators, who defected from other parties.
It has set itself modest goals for Sunday, hoping to reach 40-50 senators, and will be counting on alliances with lawmakers from other parties to back the government on a case by case basis. His party would need 180 seats in the Senate to reach the three-fifths majority in parliament.
Sunday's election is expected to consolidate the Senate's conservative majority, now composed of 142 members of The Republicans party, confirming the Senate as a counterweight to Macron, even if the National Assembly, where Macron has a clear majority, has the final say on legislation.
Jean-Luc Melenchon's far-left party 'France Unbowed,' which staged a large protest march against Macron on Saturday, has 17 deputies in the National Assembly but is not presenting any candidate to the Senate.
(Reporting by Dominique Vidalon, Elizabeth Pineau; Editing by Ingrid Melander and Toby Chopra)