* Western governments tighten financial sanctions on Iran
* Electronic transactions eyes as part of push
* EU preparing rules to clarify sanctions
BRUSSELS, Feb 23 (Reuters) - European Union governments may agree in coming weeks on rules to stop the global electronic money transfer system SWIFT doing business with Iranian banks, EU officials said on Thursday.
The new regulations are part of a push by the United States and Europe to starve the Iranian government of funds and persuade it to hold back on its nuclear programme, which they fear aims to produce bombs. Tehran says it needs atomic energy to meet its electricity needs.
Expelling Iranian banks from the Belgium-based Society for Worldwide Interbank Financial Telecommunication (SWIFT) would shut down Tehran's main avenue to making transactions with the rest of the world.
A set of regulations is now being prepared, officials said, that would state clearly that communications services related to financial transactions, such as those provided by SWIFT, are part of an EU-wide freeze on the assets of some Iranian banks and the central bank.
"Arrangements are being discussed ... and should be adopted rather quickly," one senior EU official said, adding that a final decision on whether to target SWIFT had yet to be taken.
SWIFT has already said it would comply with EU rules once European governments make it clear what they want.
Other rules due to be announced should clarify previous EU sanctions against Iran. For example, diplomats said, lists are being drawn up of equipment that cannot be sold to Iran or types of petroleum products that can no longer be imported to Europe under its oil embargo.
The discussions follow a January decision by EU governments to significantly expand sanctions against Tehran, including a ban on importing, buying and transporting Iranian crude oil.
However, the United States has also been pushing the EU to force SWIFT to evict the Iranian firms from its systems, arguing this was important to make financial sanctions work.
SWIFT, with headquarters just outside the Belgian capital Brussels, is vital to international money flows, exchanging an average 18 million payment messages per day between banks and other financial institutions in 210 countries.
The member-owned cooperative has been described as the 'glue' of the global banking system, and the value of daily payments using SWIFT is estimated at more than $6 trillion.
Nineteen banks and 25 connected institutions from Iran sent and received some 2 million messages via SWIFT in 2010. (Reporting by Justyna Pawlak. Editing by Sebastian Moffett and Maria Golovnina)