U.S. prosecutors on Friday opposed a request by accused Galleon fund founder Raj Rajaratnam and his main co-defendant for separate trials in what prosecutors have described as the biggest hedge fund insider-trading case ever in the United States.

Federal prosecutors said Rajaratnam and former New Castle Funds LLC trader Danielle Chiesi engaged in a common plan to obtain inside information from multiple sources and shared and exchanged that information with each other, according to court papers filed in U.S. District Court in Manhattan,.

Rajaratnam's and Chiesi's illegal insider trading schemes share a substantial identity of facts and participants -- Rajaratnam and Chiesi engaged in insider trading in the same stocks, during the same time period, based on the same inside information obtained from the same sources, prosecutors wrote in a memorandum.

The pair also face trial on civil fraud charges brought by the U.S. Securities and Exchange Commission along with about 20 other former traders, lawyers and executives in a purported network that stretched from Wall Street to Silicon Valley.

Prosecutors have accused Rajaratnam of making $45 million (29.6 million pounds), in profits or avoided losses, from illegal trading based on confidential tips, and they have alleged that Chiesi made $4 million.

Much of the government evidence was gathered using wiretaps and cooperators. Ten out of 21 people charged have pleaded guilty to fraud charges.

Eight of those, some of them Rajaratnam's former friends and business associates or onetime Galleon employees, have signed cooperation agreements with federal prosecutors and may be called to testify.

The case is U.S. v. Rajaratnam et al, U.S. District Court, Southern District of New York, No. 09-01184.

(Reporting by Ilaina Jonas; Editing by Jan Paschal)