This paper proposes a transcoding method for frame rate reduction in H.264 video coding standard. H.264 adopts various block types and multiple reference frames for motion compensation. When frames are skipped to reduce frame rates in transcoder, it is not easy to estimate optimum motion vectors and block types in H.264. A simple and effective block-adaptive motion vector resampling (BAMVR) method is proposed to estimate motion vector for motion compensation. In order to improve coding efficiency and visual quality, the rate-distortion optimization (RDO) algorithm is also combined with the BAMVR method in transcoder. In experimental results, rate-distortion performance and computational complexity of the proposed transcoder are analyzed for various video sequences. The proposed method achieves remarkable improvement in computational complexity compared to the full-motion estimation (ME) with RDO method.