* Criminal business one of the world's largest - U.N.
* Threatens international development goals
* Crime groups showing "impressive adaptability" - U.S.
VIENNA, April 23 (Reuters) - Crime generates an estimated $2.1 trillion in global annual proceeds - or 3.6 percent of the world's gross domestic product - and the problem may be growing, a senior United Nations official said on Monday.
"It makes the criminal business one of the largest economies in the world, one of the top 20 economies," said Yury Fedotov, head of the U.N. Office on Drugs and Crime (UNODC), describing it as a threat to security and economic development.
The figure was calculated recently for the first time by the UNODC and World Bank, based on data for 2009, and no comparisons are yet available, Fedotov told a news conference.
Speaking on the opening day of a week-long meeting of the international Commission on Crime Prevention and Criminal Justice (CCPCJ), he suggested the situation may be worsening "but to corroborate this feeling I need more data".
He said up to $40 billion is lost through corruption in developing countries annually and illicit income from human trafficking amounts to $32 billion every year.
"According to some estimates, at any one time, 2.4 million people suffer the misery of human trafficking, a shameful crime of modern day slavery," Fedotov said separately in a speech.
He also cited a range of other crimes yielding big money.
Organised crime, illicit trafficking, violence and corruption are "major impediments" to the Millennium Development Goals, a group of targets set by the international community in 2000 to seek to improve health and reduce poverty among the world's poorest people by 2015, Fedotov said.
Criminal groups have shown "impressive adaptability" to law enforcement actions and to new profit opportunities, a senior U.S. official told the meeting in Vienna.
"Today, most criminal organizations bear no resemblance to the hierarchical organized crime family groups of the past," Principal Deputy Assistant Secretary Brian Nichols said, according to a copy of his speech.
"Instead, they consist of loose and informal networks that often converge when it is convenient and engage in a diverse array of criminal activities," Nichols, of the U.S. Bureau of International Narcotics and Law Enforcement Affairs, added.
He said terrorist groups in some cases were turning to crime to help fund their operations: "There are even instances where terrorists are evolving into criminal entrepreneurs in their own right." (Reporting by Fredrik Dahl; Editing by Mark Heinrich)