SYDNEY, June 4 (Reuters) - Economists at Australia's two top lenders expect the country's central bank to shift to a "flexible" quantitative easing (QE) programme, highlighting the uncertainty over its eventual move to tapering its extraordinary stimulus.

Westpac Banking Corp and ANZ Banking Group now expect the Reserve Bank of Australia (RBA) to announce an open-ended weekly A$5 billion government bond purchase programme at its July 6 board meeting.

Both the banks were earlier predicting a third round of A$100 billion QE programme over a six-month period, identical to the first two rounds.

While they expect the RBA to continue with the current weekly pace of bond buying of A$5 billion, the two banks now believe the RBA would steer clear from committing to a total quantity.

"That model would provide flexibility, allow the RBA to more closely monitor the actions of the U.S. Federal Reserve, but certainly not appear to be 'tapering' given how much scope still exists for QE in Australia," Evans wrote in a note.

This expectation is not shared by the other two major banks though. Commonwealth Bank forecasts the RBA would halve the size of its programme to A$50 billion while National Australia Bank sees a tapered A$75 billion QE.

None of the banks expect the RBA to roll forward its three-year yield target beyond the April 2024 government bond.

RBA Governor Philip Lowe is scheduled to hold a press conference after its July board meeting in a departure from its usual practice, which, Westpac said, could be used to convince investors the central bank was still very much in the market to expand its balance sheet.

ANZ and Westpac economists said it would be premature for the RBA to begin tapering given it is grappling with anaemic inflation in an economy that is recovering rapidly from the coronavirus pandemic.

RBA Deputy Governor Guy Debelle recently noted that the "stock" of central bank purchases mattered more, rather than the "flow", adding that the RBA was well behind other central banks on that measure.

The RBA's stock of bonds is projected to reach 10% of Australia's A$2 trillion gross domestic product when the second round of QE expires in September.

That compares with 20-25% for the United States, Canada and New Zealand and 30–35% for Europe and the United Kingdom. (Reporting by Swati Pandey; Editing by Shri Navaratnam)