TOKYO (AP) _ Japanese trading company Sumitomo Corp. sued Credit Lyonnais Rouse today, accusing it of assisting a former Sumitomo employee who caused massive losses through illegal copper trades.

In a lawsuit filed in the High Court of England and Wales in London, Sumitomo is seeking about $308 million from Credit Lyonnais Rouse.

The lawsuit accuses Credit Lyonnais Rouse of dishonestly assisting Yasuo Hamanaka, the former Sumitomo employee, to make unauthorized trades that resulted in losses of $2.6 billion, Sumitomo said. It did not elaborate.

Credit Lyonnais Rouse, the London-based subsidiary of France's Credit Lyonnais, denied any wrongdoing and said it will contest Sumitomo's lawsuit.

``It considers the business relationship between the two organizations to have been conducted properly and openly in all aspects,'' it said in a statement.

Last month, Sumitomo sued UBS AG of Switzerland and Chase Manhattan Corp. of the United States demanding compensation for loans they allegedly provided to Hamanaka.

The 1996 disclosure of Hamanaka's illegal trades shook world copper markets, and raised questions about oversight at Japanese corporations.

The former star copper trader, who pleaded guilty to forgery and fraud charges, was sentenced to eight years in prison in March 1998.