* France will follow Monaco's lead on ban
* Ban would not come into force before September 2011
* Fishermen say government's position is "incoherent"
(Rewrites throughout)
By Michel Rose
PARIS, Feb 3 (Reuters) - France said on Wednesday it would support a ban on global trade in bluefin tuna, but after an 18-month delay, bowing to pressure from the fishing lobby to hold off an immediate decision on the giant fish.
France, Italy and Spain account for half of the world's total allowable catch of bluefin tuna.
Environmentalists such as Greenpeace called the delay "absurd" and said it could lead to the extinction of the fish that is prized by sushi lovers.
"Asking for 18 months to implement this measure equates to waiting until there is no more bluefin tuna before acting," Greenpeace said in a statement. "The government is buying peace with the fishermen at a time of regional elections."
Monaco has proposed protecting bluefin tuna, which can fetch up to $100,000 in Japan, by listing it under appendix I of the Convention on International Trade in Endangered Species (CITES).
France did not expect a ban to come into effect before Sept. 2011, Environment Minister Jean-Louis Borloo said on Wednesday, adding the CITES committee needed the results of a scientific study on stocks before taking a decision in July 2011.
"There is still powerful international lobbying from a big country, which has allies," he said, referring to Japan, where 80 percent of the catch is exported.
The European Union failed to make progress on bluefin tuna last year, with Greek Environment Commissioner Stavros Dimas and Maltese Fisheries Commissioner Joe Borg deadlocked over how far the EU should go to protect the fish.
EU diplomats expect to see faster progress this year under newly nominated Greek Fisheries Commissioner Maria Damanaki.
French Agriculture Minister Bruno Le Maire said on Wednesday that France would call on the European Commission to compensate fishermen for lost revenues should the ban be imposed.
Fishermen's representatives called the French position "incoherent" ahead of the regional elections in March.
"The government is really in a messy position," said Francois Wendling, head of a fishermen's trade association in Sete in southern France.
"If waiting for scientific studies is so important, why is the government giving a position now? This is purely political."
President Nicolas Sarkozy said last year he favoured a clear trade ban on bluefin tuna.
Asked if the government would stand by its position if fishermen decided to block ports as they did in Marseille last April, Le Maire said:
"French fishermen are reasonable people. But what makes them angry is when rules do not apply to everyone. France will ask for reinforced sanctions against countries which do not respect them (bluefin tuna fishing quotas)."
There are about 200 tuna boats in France, but only 28 are so-called "purse-seiners", 40-metre long high-tech boats which account for 90 percent of all French catch. Traditional fishing for domestic markets will remain possible, Le Maire said.