May 11 (Reuters) - The European Central Bank does not intend to reveal how much is being spent on its unprecedented bond-buying program because that information could assist speculators, a European monetary source said on Tuesday.

National central banks in the euro zone started buying government bonds at the behest of the ECB on Monday as a key part of efforts to prevent the debt problems of weak states from destabilising financial markets.

Details of the bond purchases remain vague, with no hint of how much central banks will buy. The monetary source, speaking on condition of anonymity, said this was intentional, since even publishing purchase totals might give fodder to speculators.

“It is not something that has a precommitted volume. It is used with a goal of stabilising markets and therefore it makes no sense to discuss specific numbers,” the source said.

“We should avoid any information which could be used for speculative attacks.”

The source said the ECB would target problem areas in the bond market, implying it would stick to bonds where yields spiked, a problem suffered by Greek, Portuguese, Spanish, Irish and Italian debt in recent weeks.

“The intention is to get again control of the unorderly markets and I think this is a goal that has been achieved remarkably in an effective way, so I think it makes sense to stay on the way we have started,” the source said.

STERILISATION

The ECB has said the bond purchases will not fuel inflation or add to the amount of money circulating in the economy because they will be offset by liquidity-absorbing measures.

But the monetary source said policymakers were still discussing the scope of these offsetting moves -- leaving open the option that not all the bond purchases would be completely sterilised.

ECB President Jean-Claude Trichet has said term deposits might be used in sterilisation efforts, and the monetary source noted the U.S. Federal Reserve had set an example by issuing bonds.

The source said he could not talk about whether the purchases would be 100 percent sterilised or go into technical details, but said the bigger the purchases were, the more need for sterilisation.

“If volumes are larger, sterilisation becomes more pressing.”

GROWTH

The source also said that while some countries would suffer under the pain of budget cuts, the euro zone as a whole would not be affected by fiscal belt-tightening.

Instead, the ECB could well revise up its forecasts for economic growth in the 16-nation region on the back of a brighter global outlook, the source said.

“For the time being I would think that we will rather have an upward revision because what we see is that world trade and therefore exports show a pretty strong development,” he said.

“If you look at the strong economies like Germany, like France, or Austria, we see that ... export performance is better than expected and therefore labour markets are better than expected. So while it’s early to say, I could imagine that we will also have upward revisions for the euro zone in its totality.”

The source said there was no reason for the ECB to change its assessment of balanced inflation risks, despite pressures from rising commodity prices, and gave no hint that the ECB might raise rates from the current 1 percent any time soon.

“Inflationary expectations are very balanced, and I don’t see a major reason how this could change.” (Editing by James Dalgleish)