By Vuyani Ndaba

JOHANNESBURG (Reuters) - Nigeria's naira will lose around a third of its value after the central bank floats the currency and adopts a new market-driven trading regime on Monday, a Reuters poll found.

The naira <NGN=D1> has been pegged at 197 to the U.S. dollar for the past 16 months but the currency trades at around 355 on the parallel market as a slump in oil revenues has hammered public finances and foreign currency reserves.

On Wednesday the central bank said it would abandon the peg in a "managed float" and the median forecast from ten analysts surveyed in the past two days suggests it will trade on Monday in a range of 275 to 300 per dollar and settle at 300 in a month.

"The rate has been kept artificially high for a long time and so we think that in a market driven system, the official rate would converge towards where the black market has been," said John Ashbourne at Capital Economics.

"But it should not go quite as low as the black market rate is currently because there will be more liquidity and dollar supply, which should prevent it from falling where the parallel rate is."

A Reuters poll in May predicted Nigeria's central bank would devalue the naira in the coming months. That survey also said the Bank would hike interest rates last month and in November to control inflation.

However, the central bank kept its benchmark interest rate on hold at 12 percent and maintained its existing cash reserve ratios for commercial banks.

Still, the naira will find support from the Federal Reserve's decision to leave its policy unchanged on Wednesday. Higher rates there tend to draw inflows away from emerging markets like Nigeria and they are expected to rise only once this year. [FED/R]

Nigeria's central bank governor said in a letter to President Muhammadu Buhari he expects the naira to settle at around 250 to the dollar.

Currency dealers and bank chiefs meet central bank officials on Friday to discuss trading under the new interbank foreign exchange regime, a treasury source said.

(Additional reporting by Ulf Laessing and Alexis Akwagyiram in Lagos, Karin Strohecker and Sujata Rao in London and Sarmista Sen in Bengaluru; Editing by Toby Chopra)