* Anticipation of ECB action keeps sterling weak versus euro * Euro near 3-week high of 79.55 pence * Stiff chart resistance seen before key 80 pence level * Pound seen staying firm vs dollar By Jessica Mortimer LONDON, Aug 29 (Reuters) - Sterling held close to a three-week low against the euro on Wednesday as the prospect of European Central Bank action to tackle the debt crisis in coming weeks buoyed demand for the single currency. The euro was at 79.43 pence, steady on the day but staying near Tuesday's three-week peak hit of 79.55 pence. Traders said month-end demand to buy euros against the pound could help it test Tuesday's high. However, the single currency was expected to face stiff chart resistance before 80 pence, including the Aug. 6 peak of 79.66 pence and the 100-day moving average at 79.98 pence. With no major UK economic data or events due, moves were expected to be limited in the run-up to a meeting of central bankers at Jackson Hole, Wyoming, beginning on Friday. "The balance of risks is for the euro to move higher until we get beyond Jackson Hole," said Adam Cole, global head of currency strategy at RBC. But sterling stayed firm against the dollar, which was weighed down by speculation that U.S. policymakers may be close to introducing more monetary easing. Federal Reserve Chairman Ben Bernanke speaks on Friday. The pound was steady at $1.5818, well above Tuesday's one-week low of $1.5754. Any hints from Bernanke on further easing would dent the dollar, potentially pushing the pound towards last week's three-month high of $1.5912. But it could face stiff resistance. Traders cited demand from central bank reserve managers to sell above $1.59. ECB ACTION Analysts and traders said Tuesday's announcement that European Central Bank President Mario Draghi was too busy to go to Jackson Hole boosted expectations he could detail a plan to tackle the debt crisis at the bank's Sept. 6 policy meeting. Speculation is mounting that the ECB will announce a bond-buying programme to lower borrowing costs for Spain and Italy. Any such measure would see the euro rally against most currencies, including sterling, traders said. Worries about the fragility of the UK economy could increase pressure to sell sterling against the euro. A survey on Tuesday showed business in Britain's dominant services sector shrank between June and August. Analysts at Morgan Stanley said they expected near-term gains in sterling against the dollar. They have a long position and target $1.6050 but take a more negative view over the medium term because of concerns about UK economic weakness. "Safe-haven flows from Europe into sterling could start to slow down if the market believes that the ECB plan will be successful in stabilising markets, leaving sterling increasingly exposed to the bearish medium-term fundamentals," they said in a note. A second reading of UK second quarter GDP on Friday showed the recession was not as deep as initially estimated but the economy still contracted by 0.5 percent. This kept alive chances the Bank of England will opt for more quantitative easing (QE) later in the year. More QE would hurt the pound as it increases the supply of the currency. (Editing by Nigel Stephenson)

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