The world's richest nations including the US, Germany, Japan and the UK are expected to press this week for a delay in the phasing out of an agricultural chemical that they had been due to abolish by the end of the year under a landmark environmental treaty to save the earth's protective ozone layer.

Signatories of the Montreal Protocol meet in Prague this week to review progress under the 1987 treaty credited with abolishing rich countries' use of CFC gases for aerosols.