Warren Buffett's Berkshire Hathaway Inc. pushed Congress to weaken proposed swaps legislation, but Democrats decided on Monday to rebuff the measure, The Wall Street Journal reported.

Berkshire did not immediately comment on the two newspaper articles. The U.S. Senate, meanwhile, is poised to debate a proposed crackdown on Wall Street that includes new rules for derivatives.

Berkshire pushed a measure in the bill that would exempt it from having to post billions of dollars of collateral, largely exempting existing derivatives contracts from proposed rules, the newspaper said. In a later article, it reported according to people familiar with the matter that that proposal was killed.

As of year end, Omaha, Nebraska-based Berkshire had about $63.1 billion of derivatives exposure. Roughly 60 percent was tied to long-term contracts whose value depends on the performance of major equity market indexes.

The company argued that it is healthy enough to cover its obligations, especially given that it has $20 billion of cash, and should not have to modify existing contracts, the newspaper said.

In 2003, Buffett labeled derivatives "financial weapons of mass destruction."

He has long distinguished Berkshire's derivatives, saying the company gets billions of dollars of upfront premiums to invest, is not generally required to post collateral, and has a strong enough balance sheet to make good on its obligations.

According to the newspaper, David Sokol, chairman of Berkshire's MidAmerican Energy Holdings Co. unit, has been meeting scores of government officials, including several senators, to argue Buffett's case.

Sokol is considered by many the leading candidate to eventually replace Buffett as Berkshire's chief executive.

Senator Ben Nelson, a Nebraska Democrat, initially helped push the provision into a bill passed by the Senate Agriculture Committee last week, according to the paper.

Nelson broke with party ranks on Monday, voting against opening Senate debate on the proposed bill.

The head of the top U.S. futures regulator said Monday he interprets the draft bills, from the House and the two Senate committees, as exempting contracts from the new rules if they were entered in the past.

"The House-passed bill only mandates clearing and trading after the President signs the bill, or actually after rule-writing," Gary Gensler, Chairman of the Commodity Futures Trading Commission, said at the Reuters Global Financial Regulation Summit in Washington D.C.

"I think that's what the Senate Agriculture and Senate Banking bill does as well, and that there's legal certainty that if you enter into a trade in 2005, that that transaction is still enforceable today, if it's still outstanding."

Gensler did not comment specifically on collateral requirements.