WASHINGTON (Reuters) - The United States, one of the world's biggest plastic makers, will support a global treaty calling for a reduction in how much new plastic is produced each year - a major shift from its earlier calls to leave such decisions up to each country, a source close to US negotiators told Reuters on Wednesday.

The change puts the U.S. in direct opposition to countries like Saudi Arabia and China. They have argued that the hoped-for UN treaty, which negotiators are scheduled to conclude at a November summit in Busan, South Korea, should ignore questions of production and focus on downstream measures such as encouraging recycling and changing packaging design.

(Reporting by Valerie Volcovici; Editing by Chizu Nomiyama)

By Valerie Volcovici