* Regular rate-setting meeting due on Sept. 15
* 20 of 23 analysts expect c.bank to cut rate to 8.5 pct
* Inflation reading already slipped below 4 pct target
* C.bank seen cutting rates further by year-end
MOSCOW, Sept 11 (Reuters) - The Russian central bank is expected to cut its key rate to 8.5 percent on Friday, catching up with a rapid slowdown in inflation, a Reuters poll showed on Monday.
Twenty of 23 analysts and economists polled said they expected the central bank to lower the key interest rate by 50 basis points from the current 9.0 percent.
The rate cut is widely expected as annual consumer inflation reading slipped to 3.3 percent in August, below the central bank's ultimate target of 4 percent.
Inflation, once stubbornly high at nearly 17 percent in early 2015, recently slowed to post-Soviet lows thanks to what the central bank calls a "moderately tight monetary policy" along with a seasonal drop in prices for fruit and vegetables.
"Given that the CBR missed the July cut, we think that it will now deliver a deeper 50 basis point cut..., followed by more gradual 25 basis point cuts this year," Morgan Stanley analysts said in a note.
The number of those who believe in imminent rate cuts also increased after the latest round of U.S. sanctions, imposed in August and designed to punish Moscow for its alleged meddling in 2017 presidential elections in the United States, proved to have a limited impact on Russia.
Central bank officials confirmed the market view last week by saying they would choose between trimming the key rate by 25 or 50 basis points when deciding to slash the cost of borrowing for the fourth time this year on Friday.
Three out of 23 analysts polled by Reuters predicted a 25 basis point cut, pointing to inflation risks related to a pick up in food prices and global political tensions.
Rosbank, a subsidiary of Societe Generale, said the central bank will opt for caution on Friday and will likely prune the rate by only 25 basis points, while promising a loser monetary policy in its accompanying comments.
Lower rates are needed to make lending cheaper to help the Russian economy recover further after two years of recession, caused by a drop in prices for oil, the country's key export, and Western sanctions that were levied on Moscow for its role in the Ukrainian crisis.
Expectations of further easing of monetary policy, which would eventually take the key rate to the central bank's desired range of 6.5-7 percent, should also have a positive impact on the economy.
A separate Reuters poll of analysts and economists conducted in late August showed the central bank, which will hold three rate-setting meetings by the end of the year, was expected to bring the key rate to 8.25 percent by end-2017.
The stronger rouble, which firmed by around two percent against the dollar so far this month, would help the central bank to rein in inflation and thus should prop up consumer demand, Russia's key economic growth driver.
(Editing by Katya Golubkova and Toby Chopra)