UPDATE 1-UN panel chair says may need to adjust HFC projects

* UN offset scheme chair says looking at possible loophole

* Says panel could decide to adjust HFC-23 offset issuance

* Executive willing to take firm "drastic action" if needed

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By David Fogarty

SINGAPORE, June 22 (Reuters) - The most profitable projects under a U.N. carbon offset scheme may have claimed excessive emissions cuts and the amount issued to them could be adjusted, the head of a panel that governs the scheme said on Tuesday.

The $2.7 billion scheme under the Kyoto Protocol allows developing countries to claim carbon offsets for emissions cuts, and sell these to polluting companies in the developed world.

The most lucrative projects are those that destroy a very powerful greenhouse gas called hydrofluorocarbon-23 (HFC-23), earning them a large number of offsets in return.