NEW YORK (Reuters) - Galleon Group founder Raj Rajaratnam urged a federal judge on Friday not to allow the U.S. Securities and Exchange Commission to add new charges against him in a widening insider trading probe.

The SEC asked U.S. District Judge Jed Rakoff on Wednesday to let it amend for a second time its civil complaint against Rajaratnam and others, in what investigators have described as the largest hedge fund insider trading case ever.

In the Wednesday filing, the SEC alleged Rajaratnam paid former McKinsey & Co official Anil Kumar for insider tips and used them to generate almost $20 million of illegal profits for Galleon.

The SEC sought the amendment after Kumar pleaded guilty on January 7 to fraud and conspiracy, saying Rajaratnam paid him $1.75 million in exchange for tips on McKinsey clients.

In a response on Friday, lawyers for Rajaratnam said allowing an amended complaint would "seriously prejudice" their client and said the SEC should have raised its claims sooner.

They also said Rajaratnam is on track to be deposed in early March and that a new complaint would delay the case, first announced by the SEC and the U.S. Department of Justice last October 16. The SEC case is scheduled for trial on August 2.

John Dowd, Rajaratnam's lead lawyer, wrote that the latest request "is a product of the SEC's rush to file this case at the same time as the United States Attorney's Office filed its criminal complaint so that they could hold a joint press conference trumpeting their purported achievements."

SEC representatives were not immediately available after business hours for comment.

Rajaratnam, widely described as a billionaire, was indicted last month for insider trading that prosecutors have said may have led to $41 million or more of illegal profits. He pleaded not guilty.

The SEC has said a hearing on its request is scheduled for the afternoon of January 25 before Rakoff.