* Earlier start date examined for EU 'bail-in' rules
* Fears that sudden shift could upset markets
* ECB's Constancio says start date should be reconsidered
BRUSSELS, Jan 31 (Reuters) - Bondholders who lend to European banks that get into trouble could face losing their money from 2015, three years earlier than planned, euro zone officials said.
Under a German proposal, the EU would bring forward a plan to shield taxpayers from bail-out costs by handing losses to some bondholders if needed and keep failing banks going.
Under the existing timetable for EU legislation, the socalled "bailing in" process proposed by the European Commission is due to take effect from 2018.
The radical plan would mean that when banks need to be shut, the costs would be lower for their home countries and potentially also for the euro zone's joint rescue fund, the European Stability Mechanism.
But it risks scaring investors away from the multi-trillion-euro market for unsecured bonds.
"The proposal for bailing in had first been from 2018 onwards," said a diplomat familiar with talks on the proposal who confirmed that talks were now under way for a 2015 start.
The new law is designed to draw a line under the region's financial crisis, more than five years after Germany's IKB became the first casualty of a crash in U.S. subprime loans that later sucked in Ireland, Greece and now Cyprus.
The proposal, discussed by officials from member states at a meeting this week, could help take Germany and other strong countries off the hook for the clean-up of the wider European banking sector.
But EU banks, which have $1.9 trillion of outstanding unsecured bonds, are lobbying against any faster or wider application of bail-in rules inflicting losses on investors.
They fear it would rattle markets and compound their borrowing difficulties.
"If you do it too soon, you risk making it even more difficult for banks to raise funding," said Carsten Brzeski, an economist with ING.
"The technical question of bailing in bank bondholders is very similar to the question of haircuts on owners of sovereign debt and the introduction of collective action clauses because the losses are not voluntary."
The proposal is intended to prevent EU countries taking a variety of approaches to deal with struggling banks and bondholders and to discourage reckless risk-taking by banks that expect to be bailed out by taxpayers again.
The European Central Bank, which will take on the task of supervising big banks in the euro zone from early 2014, is also pushing for a system of closing laggard banks.
For this to work, a system of 'resolution' needs to be put in place to close banks the ECB deems too weak to survive. This entails costs too high for EU member states to bear alone.
Having bail-in powers in place earlier would complement that framework.
ECB Vice President Vitor Constancio signalled on Thursday that he favoured an earlier start date for 'bail-in', saying the 2018 proposal should be reconsidered.
But officials in the early stages of talks on the subject are wary of any fall-out from such a sudden adjustment.
"It can be done very easily. You just have to take out the deadline of 2018. The only thing that's difficult to predict is the market reaction. Psychology is something that is very difficult to calculate," said an EU official familiar with the matter. (Editing by Tom Pfeiffer)