MELBOURNE, March 21 (Reuters) - Australian Strategic Materials said on Thursday it has received a letter of interest (LOI) for a debt funding package of up to $600 million from the Export-Import Bank of the United States to support construction of its Dubbo rare earths project.

If confirmed, this would be the first U.S. investment in rare earths processing in Australia and comes as Western nations build supply chains outside of China to produce magnets used in sectors from windfarms to defence.

The Australian rare earths developer has plans to build out its Dubbo rare earths mine and processing plant 400 kilometres (250 miles) north west of Sydney for which it is seeking customers and finance.

It last year agreed to sell neodymium iron boron alloy from its South Korean metals plant to U.S.-based rare-earth magnet maker Noveon Magnetics Inc.

Australia last week said it would provide up to A$840 million ($550 million) for a combined rare earths mine and refinery in the country's Northern Territory, owned by Arafura Rare Earths. (Reporting by Ayushman Ojha and Melanie Burton in Mekbiyrne; Editing by Krishna Chandra Eluri and Josie Kao)