* EU legal experts say GM crop plans risk WTO challenges
* Opinion backs up criticism of plans from some EU states
* Governments due to discuss legal opinion this week
BRUSSELS, Nov 8 (Reuters) - EU legal experts "seriously doubt" that plans to let European Union member states decide for themselves to grow or ban genetically modified (GM) crops are in line with global trade rules, officials said on Monday.
The European Commission made legal proposals in July to let governments to make their own decisions on the controversial crops, in a bid to break a longstanding EU deadlock on new GM product approvals.
But a new opinion from the EU Council of Ministers' legal service could deal a fatal blow to the plans, after several EU governments already expressed fears that the draft law risks breaching World Trade Organisation (WTO) rules.
"Everything to do with WTO compatibility in the legal opinion is not positive at all," one EU source told Reuters.
A key concern raised by the legal experts is how governments would justify a cultivation ban after the Commission had ruled out environmental or health grounds for prohibitions.
"Economic arguments cannot be relied upon ... so the obvious remaining candidate would therefore be ethical reasons," the opinion stated, according to an EU official.
But ethical arguments are unlikely to be accepted by the WTO or the European courts as grounds for a ban, as livestock farmers in most EU countries already feed animals with imported GM products, thus undermining the argument, the opinion added.
As a result, national cultivation bans based on ethical criteria risk being either rejected by the European Courts or challenged in the WTO, the experts concluded.
The legal opinion will be presented to EU government experts in Brussels on Thursday, in a meeting that could confirm majority opposition to the plans among the bloc's 27 member states.
France, Italy and Spain have all expressed doubts over the Commission's plans and want decisions on GM cultivation to continue to be taken collectively at EU level.
(Reporting by Charlie Dunmore, editing by Rex Merrifield)