Lehman Brothers Holdings Inc sued Nomura Holdings Inc <8604.T> on Friday, saying the Japanese bank is not entitled to recover $760 million it claims, and instead owes it tens of millions of dollars.

In complaints filed in Manhattan bankruptcy court, Lehman said Nomura arbitrarily changed its method to calculate amounts owed under two swap agreements.

It said the new, higher sums reflect egregious inflation, and a desire by Nomura to secure a windfall from Lehman's bankruptcy at the expense of deserving creditors.

Nomura has filed more than $2 billion of claims against two Lehman entities over swap agreements, according to the two complaints.

We disagree with their arguments, and fully expect to be paid in due course, a Nomura spokesman said.

According to Friday's complaints, Nomura had entered into swap agreements with Lehman concerning some 3,190 derivatives transactions between the companies.

Lehman said the agreements ended no later than when it filed for bankruptcy protection on September 15, 2008.

The company said that in early September, Nomura calculated that it owed Lehman $248 million under one agreement and $90 million under the other, and transferred $338 million of credit support to Lehman to reflect this.

But Nomura later claimed that Lehman actually owed it $444 million under the first agreement, and that it owed Lehman just $42 million under the second agreement, the complaints show.

Lehman said the new sums reflected an arbitrary change in Nomura's methodology, plus the impact of transactions tied to Icelandic banks that defaulted in November 2008, two months after the first swap agreement supposedly ended.

According to the complaints, Nomura's claims include the $338 million, the $444 million, various other payments, interest and legal fees, less the $42 million.

Such claims are premised on purported valuations and calculations that are commercially unreasonable, divorced from economic reality, and bear no relation to any actual damages or losses suffered by Nomura, Lehman said.

Not only is Nomura not entitled to a single cent from the debtors, but instead it is Nomura that owes the debtors tens of millions of dollars, it added.

Nomura acquired European and Asian assets from Lehman shortly after the latter filed for Chapter 11 protection.

Lehman's bankruptcy remains by far the largest in U.S. history. Last month, it said creditors' claims should be reduced to $605 billion, and that allowed claims might ultimately decline to $260 billion.

The case is In re: Lehman Brothers Holdings Inc et al, U.S. Bankruptcy Court, Southern District of New York, No. 08-13555.

(Reporting by Jonathan Stempel, editing by Matthew Lewis)