* FTSE 100 up 0.4 percent * Fed chairman-designate defends bond-buying programme * Centrica weakens, analysts cut target prices By Tricia Wright LONDON, Nov 15 (Reuters) - Britain's top shares rose on Friday, bolstered by the promise of continued U.S. monetary stimulus, with energy stocks and miners posting the biggest gains. The mood in the markets was lifted after the Federal Reserve's chairman-designate Janet Yellen defended the bank's quantitative easing programme on Thursday, dispelling concerns about an early reduction of the asset purchases. With risk appetite boosted by the comments, cyclical stocks such as miners and oils found favour, helping drive the FTSE 100 up 26.74 points, or 0.4 percent, to 6,692.87 points by 1216 GMT. The QE programme has helped the UK benchmark index, which has risen nearly 20 percent as investors have moved out of safe bonds and into higher yielding assets, such as stocks. This has left the index trading on a 12-month forward price/earnings ratio of 12.7 times, above its 10-year average of 12, Thomson Reuters Datastream shows. Some traders saw scope for a sell-off. "As you would be hard pushed to find many bears out there due to the 'Yellen effect', the contrarian in me feels it's time to bet against the trend with equities looking overbought," Mike McCudden, head of derivatives at Interactive Investor, said. But Charles Stanley analyst Bill McNamara said 6,600, around the index's 50-day moving average and which represents a 38.2 percent retracement of the recent rally, looked like a key support level. Utility group Centrica, off 2.4 percent, pinned back the FTSE, falling for a second day as a string of analysts cut their target prices for the stock after a profit warning on Thursday. "On one hand, profits are being eroded by competitive pressures in energy retail and power generation; on the other the ...rhetoric in the media is hostile due to perceived profiteering," JPMorgan said in a note. "Until the public and political climate becomes more constructive, we see limited share price upside for either Centrica or (peer) SSE." Shares in SSE slipped 0.6 percent.