SHANGHAI, March 17 (Reuters) - China stocks ended flat on Wednesday as investors shifted focus to the outcome of a U.S. Federal Reserve policy meeting, to see if the central bank could start raising interest rates sooner than expected. ** Fed policymakers are expected this week to forecast that the U.S. economy will grow in 2021 at the fastest rate in decades as the COVID-19 vaccination campaign gathers pace and a $1.9 trillion relief package washes through to households. ** At the close, the Shanghai Composite index was down 0.03% at 3,445.55, while the blue-chip CSI300 index was up 0.42% to 5,100.86. ** The financial sector sub-index was lower by 1.42%, the consumer staples sector rose 1.58%, the real estate index fell 0.96% and the healthcare sub-index gained 0.49%. ** The smaller Shenzhen index ended up 0.97% and the start-up board ChiNext Composite index was higher by 1.198%. ** Gains were driven by agricultural shares after the government unveiled measures to support the development of Taiwan-funded companies in agriculture and forestry in mainland China. ** The sector also gained support after the central Henan province said it would strictly prevent illegal genetically modified seeds from entering the market this year. ** At the close, Winall Hi-tech Seed Co Ltd jumped 7.7%, Hefei Fengle Seed Co Ltd leapt 6.4%, and Zhongnongfa Seed Industry Co Ltd jumped 4.9%. ** Some investors said they would closely watch the first high-level, in-person contact later this week between Beijing and Washington since U.S. President Joe Biden took office. Sino-U.S. relations have been one of the key factors influencing Chinese financial markets over the past few years. ** Separately, Chinese companies targeted by a sweeping investment ban imposed by former U.S. President Donald Trump are considering suing the U.S. government after a federal judge on Friday suspended a similar blacklisting for Beijing-based smartphone maker Xiaomi. (Reporting by Winni Zhou and Andrew Galbraith; Editing by Ramakrishnan M.)