(Adds c.bank source, dealer quote, details)
By Yelena Fabrichnaya and Gleb Bryanski
MOSCOW, Dec 5 (Reuters) - Russia's central bank moved to widen the rouble's trading band on Friday, opening the door to a fourth devaluation within a month, and the currency weakened to 31.62 from 31.30 against its dollar/euro basket.
The move comes one day after Russia's gold and foreign exchange reserves posted their first weekly rise in two months, enabling Prime Minister Vladimir Putin to say the cash will help the economy weather the global crisis.
The central bank was forced to let the rouble depreciate in three one-percent steps against a euro-dollar basket last month as prices for oil, Russia's main source of foreign currency revenues, fell sharply.
A source in the central bank confirmed the trading band had been widened further. Dealers said the regulator had changed the level at which it intervenes to support the rouble.
"Looks like they have found a new level, otherwise they would not sell (dollars). I think it will be another 30 kopecks (0.3 roubles)," said Gazprombank's chief trader Viktor Kholoshnoi.
The rouble traded at 31.5647 against the basket at 1125 GMT.
The central bank runs a managed float of the rouble, keeping it within a corridor against the basket, made of 0.55 dollars and 0.45 euros. Given low oil prices and persistent capital outflows, the rouble will tend to weaken after a band widening.
SCEPTICAL
Economists polled by Reuters last month expect the rouble to weaken further against the basket to 33.44 by the end of 2009. The rouble is down by 20 percent from its July peak against the dollar, reflecting broad-based strengthening of the greenback.
The central bank declined to comment on the latest move officially. Economists, meanwhile, are split over what the central bank should do.
Troika Dialog analyst Evgeny Gavrilenkov said a large one-time devaluation would be a useful step towards the rouble's float, proclaimed by the central bank as a medium-term target, and a weaker currency would help industry. Others disagreed.
"We are sceptical about the possibility of bigger rouble devaluation as it would fuel inflation, and potentially lead to rising social tensions," said ING analyst Tatiana Orlova.
Russian households closely watch the dollar exchange rate. With the central bank data showing an "unprecedented" $10.3 billion in net demand for foreign currency in October, confidence in the government's anti-crisis measures is at stake.
The government is also facing a problem channelling the money it pumps into the banking sector to enterprises with spreads between official and market interest rates at over 10 full percentage points.
The central bank has accompanied some of its devaluation moves by rate hikes, gradually moving official interest rates in real terms out of the negative territory where they have been in recent years.
On Thursday it set a higher-than-expected 8 percent interest rate at a two-week deposit auction, signalling a possibility of a further hike on Friday after a scheduled board meeting. Some analysts also questioned the logic behind the central bank's move one day after the increase in reserves.
"Does it make sense? Yesterday the central bank told the market that reserves would start to increase again and now they give in to obvious depreciation pressure again. That is a contradiction," said Ulrich Leuchtmann from Commerzbank.
"The situation becomes more unclear. Certainly not an environment to attract foreign capital," Leuchtmann added. The central bank spent $57.5 billion in Sept-Oct to support the rouble and carried out interventions throughout November. (Additional reporting by Andrei Ostroukh and Toni Vorobyova; Reporting by Yelena Fabrichnaya, writing by Gleb Bryanski; Editing by Ruth Pitchford)