UPDATE 3-French ports are headed for paralysis-union

(Recasts with CGT letter)

By Muriel Boselli and Jean-Francois Rosnoblet

PARIS, April 17 (Reuters) - The French port union, part of the CGT federation, warned on Thursday that ports could be crippled in a stand-off with the authorities over reforms.

A 24-hour strike at France's biggest oil port of Fos-Lavera disrupted on Thursday the traffic of four oil tankers while strikers at the Nantes Saint-Nazaire port blocked nine ships.

"Ports are headed for paralysis," the CGT said in an open letter to French President Nicolas Sarkozy. "We ask you to intervene so that the project is delayed and transformed," the union said, adding that it was better to have a reform that was understood and backed than an endless struggle.

The strikes in both ports come after France's national port union called on workers last week to stage 24-hour strikes on a weekly basis to protest against government plans to privatise loading activities at state-run ports. It is up to individual ports to decide on which day to take action.

Private firms operating at the ports say this is the worst kind of strike action because it is on-going, creates confusion, and pushes customers to use other European ports.

"It's better to have a port blocked for eight days in a row than a messy strike," an official from a body representing private port firms told a news conference.

The strike at the Fos-Lavera terminal was disrupting the loading operations for eight ships, including four oil tankers, one gas tanker and two chemical cargo ships, the port said.