* VRT says two reactors may remain offline until spring
* Says plants may even need to be halted permanently
* GDF spokesman says tests inconclusive so far
* GDF shares down more than 3 pct (Recasts with share reaction, adds background)
BRUSSELS, Aug 20 Shares in GDF Suez fell on Wednesday after Belgian state broadcaster VRT reported that two Belgian nuclear reactors owned by the French utility's unit Electrabel may remain offline until spring and may even need to be halted permanently.
Shares in GDF Suez were down 3.4 percent by 1008 GMT, the biggest losers on the CAC 40 index of French blue chips .
"The market's reaction is all the stronger given that some were hoping for a restart at the start of next year," a Paris-based trader said.
"A restart at the spring of 2015 was not very reassuring in the first place, but the prospect of a permanent closure is clearly a negative sign," the trader added.
GDF Suez said it was too early to reach conclusions.
"Gradual tests done on Doel so far do not allow to draw definitive and comprehensive conclusions either way," a spokesman for GDF Suez in Paris said, adding that tests would continue until the autumn, when the group would submit a report to the regulator, which will then make a decision.
The Belgian nuclear regulator had ordered production to be stopped at the 1,008-megawatt (MW) Tihange 2 reactor and the 1,006-MW Doel 3 reactor in 2012 after finding indications of cracks in their core tanks.
After reopening in May 2013, the reactors were closed again in March this year for further tests after inspections uncovered irregularities in the strength of the tanks.
The interim results of the tests, which are not yet completed, show the tanks are weakened by the cracks and may need to remain closed until spring or may even remain shut permanently, VRT reported on Tuesday citing unnamed sources.
Electrabel was not immediately available for comment.
With another reactor, Doel 4, also closed because of damage to its turbine, just over 3 GW of Belgian nuclear capacity is offline, more than half of the total.
GDF Suez warned last month that the closure of the first two Belgian plants would push its 2014 group net recurring income to the lower end of its forecast range of between 3.3 billion euros ($4.4 billion) and 3.7 billion.
Nuclear power provides about a third of the European Union's electricity generation, but the 28-nation bloc's 131 reactors are well past their prime, with an average age of 30 years, which could lead to more prolonged outages over the next few years. (1 US dollar = 0.7529 euro) (Reporting by Robert-Jan Bartunek and Alexandre Boksenbaum-Granier in Paris; Writing by Michel Rose; Editing by Andrew Heavens and David Holmes)