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By Grant McCool

NEW YORK - U.S. prosecutors on Thursday used a profanity-laced phone tap of accused hedge fund manager Raj Rajaratnam and his brother to try and prove he had inside information on a deal before it appeared in a newspaper article.

The digitally-recorded FBI audio was among dozens played so far in the biggest Wall Street insider trading trial in decades in which Galleon Group founder Rajaratnam, 53, is the central figure.

The clip was introduced into evidence in Manhattan federal court during testimony by former Intel Corp executive Rajiv Goel, a friend of Rajaratnam's for 17 years who has pleaded guilty and is a key government witness.

Goel has admitted to tipping Rajaratnam on March 19, 2008 about a new wireless network venture between Clearwire Corp and Sprint Nextel Corp in which Intel would invest $1 billion.

Prosecutors accuse Rajaratnam of buying 125,800 Clearwire shares on March 24 based on inside information.

Oh dude, we're f-----, Rajaratnam's brother Rengan, also a fund manager, said on the March 25, 2008 call. It just hit the Wall Street Journal.

Rengan Rajaratnam went on to describe some details in the article, including possible capital commitments from Intel, Comcast Corp and Google Inc .

O.K. S---, Rajaratnam responded.

So, I don't know how much you got in today, but I think is gonna rip tomorrow, Rengan Rajaratnam was heard telling his brother.

Goel tipped Rajaratnam with similar details, according to another phone tap in government evidence that has also been played to the 12-member jury. The Clearwire venture was announced on May 7, 2008.

Rajaratnam's defense is that his trades were based on his own research and publicly available information.

In cross-examination of Goel, 52, that began on Thursday, a lawyer for Rajaratnam attacked his credibility.

The government accuses Sri Lankan-born Raj Rajaratnam of making $45 million in illicit profit. If convicted, he could face up to 20 years in prison.

The government says Rengan Rajaratnam, founder of Sedna Capital Management, conspired with his older brother, but he is not among 26 people who have been criminally charged. Nineteen pleaded guilty, including Indian-born Goel.

In the cross-examination of Goel, defense lawyer Terence Lynam said Goel omitted Swiss bank account information from his tax returns and cut a deal, a plea bargain in hopes of leniency for admitting to insider trading.

I don't understand the expression, sir, Goel said. I pleaded guilty.

Goel, the second friend-turned-government-witness to take the stand after former McKinsey & Co management consultancy executive Anil Kumar two weeks ago, admitted on the stand on Tuesday that he violated his obligations of confidentiality to Intel.

His testimony was suspended on Wednesday when the government called Goldman Sachs Group Inc chief executive Lloyd Blankfein, who testified that former Goldman director and McKinsey worldwide head Rajat Gupta violated bank confidentiality by leaking secrets to Raj Rajaratnam.

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

(Reporting by Grant McCool, editing by Dave Zimmerman)