* Shanghai stocks down, blue-chip CSI300 index falls
* Gains in Shanghai stocks led by Hna Innovation Co Ltd
* Losses led by Zhejiang XinAn Chemical Industrial Group Co Ltd
* China's A-shares at 30.09 percent premium over H-shares
SHANGHAI, March 7 (Reuters) - China stocks reversed gains from earlier in the session to end lower on Wednesday, as fears of a trade war were rekindled amid the departure of Gary Cohn, a key advocate for free trade in the White House.
** Economic adviser Gary Cohn, seen as a bulwark against protectionist forces within U.S. President Donald Trump's administration, said on Tuesday he would resign, a move that came after he lost a fight over Trump's plans for hefty steel and aluminium import tariffs.
** "For the moment, investors shall be wary of the impact from Trump's (protectionist) tariff comments," Guosen Securities wrote in note.
** Most sectors lost ground on Wednesday, while banking firms gained as the regulator planned to cut lenders' bad debt buffers.
** "The (banking regulator's) move could bolster investor confidence in banks, as worries over their bad debts would gradually ebb," said Gao Ting, head of China strategy at UBS Securities.
** At the close, the Shanghai Composite index was down 0.5 percent at 3,271.67.
** The blue-chip CSI300 index was 0.75 percent lower, with its financial sector sub-index down 0.41 percent, the consumer staples sector falling 1.35 percent, the real estate index sliding 1.59 percent and healthcare sub-index losing 0.83 percent. An index tracking major materials firms was also down 1.1 percent.
** The smaller Shenzhen index ended down 0.77 percent and the start-up board ChiNext Composite index was weaker by 0.69 percent.
** The largest percentage gainers on the main Shanghai Composite index were Hna Innovation Co Ltd up 10 percent, followed by Shanghai Tianchen Co Ltd gaining 9.99 percent and Tibet Tourism Co Ltd up by 9.99 percent.
* The largest percentage losers on the index were Zhejiang XinAn Chemical Industrial Group Co Ltd down 8.32 percent, followed by Shandong Lukang Pharmaceutical Co Ltd losing 6.12 percent and 360 Security Technology Inc down by 4.9 percent.
** About 16.87 billion shares were traded on the Shanghai exchange, roughly 83.3 percent of the market's 30-day moving average of 20.24 billion shares a day. The volume in the previous trading session was 19.54 billion.
** As of 07:02 GMT, China's A-shares were trading at a premium of 30.11 percent over the Hong Kong-listed H-shares. (Reporting by Shanghai Newsroom; Editing by Biju Dwarakanath)