* Sept M3 money supply growth 1.0 pct vs 1.3 pct forecast
* Loans to private sector up 1.2 pct vs 1.4 forecast
* Data shows ECB stimulus still warranted - analysts
* Euro zone base rate seen unchanged well into 2011
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FRANKFURT, Oct 27 (Reuters) - Growth rates in money supply and private sector loans in the euro zone were sluggish in September, supporting the European Central Bank's careful approach to winding down measures designed to boost lending activity.
Underlining the still fragile nature of the single currency zone's economic recovery, loans to the private sector rose 1.2 percent year-on-year, ECB data showed on Wednesday, missing a Reuters forecast for 1.4 percent growth.
M3 money supply, a measure of cash readily available to spend which the European Central Bank sees as a leading indicator for inflation, rose 1.0 percent on an annual basis, versus expectations for a 1.3 percent rise.
Wednesday's figures are watched chiefly for signs that lending to companies and consumers is recovering from the banking sector shocks that began in 2008 and that the ECB's huge quantities of emergency liquidity for the sector are finally being passed on.
"The fact that broad money and overall credit growth have moved back into positive territory is encouraging," said Martin van Vliet from ING.
"But the still sluggish growth rates highlight the underlying fragility of the economic recovery.
"The ECB seems well advised to take a cautious approach towards unwinding its monetary stimulus measures."
A Reuters poll on Tuesday forecast the European Central Bank would allot 33 billion euros ($45.9 billion) at its first indexed three-month refinancing operation on Wednesday, a key test of efforts to wean banks slowly off support.
The ECB said loans to households rose 2.8 percent higher from a year earlier, the sixth rise in a row and only just down from August, when it grew at fastest rate in more than a year.
Loans to companies -- the missing link in the recovery so far -- were still declining in annual terms, but the 0.6 percent fall was less than the -1.1 percent figure for August.
"There is still significant concern over the general ability and willingness of banks to provide the necessary credit to support improving economic activity," said Howard Archer at Global Insight.
"Consequently, while there has recently been some talk about the ECB's exit plans, we suspect that the bank is likely to continue to retain some emergency liquidity measures for some time to come."
The subdued M3 data suggested the ECB would likely keep interest rates down at record lows of 1.0 percent "deep into 2011", he said.
(Reporting by John Stonestreet, London Treasury Desk; Editing by Patrick Graham, +44 207 542 4441)