LONDON (March 3): STERLING is becoming scarce in many parts of the world. Its growing scarcity is having wide effects and is likely to have more. The strengthening of sterling is already making serious difficulties for some British exports, because some overseas markets have less sterling with which to pay them. For the same reasons, it should tend to reduce the price of Australian wool, Indian jute and many other sterling commodities. Attention has been directed to the phenomenon of sterling scarcity by the sequels to the recent speech by Mr Christopher Mayhew, the Under-Secretary of State for Foreign Affairs, and by other developments in the past few days. Speaking at Lake Success, Mr Mayhew said that Britain was at last approaching an overall balance of overseas payments. Unlike Mr Mayhew's speech, the fact that, rather suddenly, Britain has started to earn a large surplus of soft currencies has attracted much less attention. This is simply the other side of her dollar deficit. Britain is exporting twice as much as she imports and has balanced her trade accounts with the world as a whole.