NEW YORK (Reuters) - The trustee overseeing the liquidation of Bernard Madoff's investment firm might sue about 1,000 victims whom he believes profited improperly from doing business with the now-imprisoned Ponzi schemer.

Irving Picard, the court-appointed trustee, "could sue" about half of the estimated 2,000 former Madoff clients whom he considers "net winners," a spokesman said.

Picard has until December to file such clawback lawsuits, marking the two-year anniversary of Madoff's December 11, 2008 arrest and the start of related criminal and civil proceedings.

While Picard would prefer to settle, "we have received few responses, if any, to our overtures", the spokesman said.

Picard earlier revealed his possible litigation in an interview with The Wall Street Journal.

In March, US Bankruptcy Judge Burton Lifland sided with Picard in rejecting an argument by many Madoff victims that their claims be assessed based on their November 30, 2008 account statements, even if the amounts shown were fictitious.

"To the extent possible, principal will rightly be returned to net losers rather than unjustly rewarded to net winners under the guise of profits," Lifland wrote.

Picard is a partner at the law firm Baker & Hostetler LLP, and as trustee is trying both to recover money for Madoff victims and to assess how much they deserve.

Through July 23, Picard had rejected 10,996, or 84 percent, of the 13,165 claims he had reviewed. He has allowed $5.55 billion of claims. Picard has said that through March 31 he had recovered more than $1.5 billion of assets for victims.

Madoff, 72, pleaded guilty in March 2009 to orchestrating an estimated $65 billion Ponzi scheme. He is serving a 150-year sentence in a North Carolina federal prison.