UPDATE 1-Swiss National Bank policy to stay loose to curb franc - Maechler

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LAUSANNE, Switzerland, Aug 28 (Reuters) - The Swiss National Bank has to keep monetary policy loose to counter demand for the safe-haven Swiss franc at a time of heightened global uncertainty, SNB governing board member Andrea Maechler said on Wednesday.

Addressing an economic conference, she stressed the central bank's willingness to intervene on currency markets and keep interest rates negative to help reduce the attractiveness of the franc, which she said was very highly valued.

Record levels of sight deposits at the Swiss National Bank suggest the central bank has been stepping up intervention on foreign exchange markets to rein in the franc, which has touched two-year highs against the euro.

"We think that the franc remains at a very high value, absolutely. That's why... we need an expansionist monetary policy... but yes it's clear there are risks," she said.

Asked if the SNB's balance sheet could ever get too big, she said the central bank always weighed the pros and cons of intervening.

"We need to have a sustainable monetary policy and keep our margin of manoeuvre," she said.

The franc's ascent comes against the background of more dovish approaches by other major central banks, signals of a global economic slowdown, the U.S.-China trade war, Italy's unsettled government and the growing risk of Britain crashing out of the European Union without a deal.

The SNB holds its quarterly monetary policy assessment on Sept. 19, a week after European Central Bank policymakers are expected to loosen policy as a way to spur a faltering economy and below-target inflation.

(Reporting by Tom Miles, Editing by Michael Shields)