* Sherpa, Transparency Intl accuse Ben Ali of corruption
* Lawyer says French asset-tracking measures insufficient
PARIS, Jan 17 (Reuters) - French rights groups Sherpa and Transparency International France will file legal complaints against Tunisia's ousted president for corruption and misuse of public funds to ensure his assets in France are frozen, the groups said on Monday.
Zine al-Abidine Ben Ali fled his country on Friday after 23 years in power, folding under the pressure of weeks of violent street protests over unemployment, high food prices and the authoritarian nature of his regime.
The case to be lodged in the next few days by Sherpa and the French subsidiary of Berlin-based corruption watchdog Transparency International accuses Ben Ali of corruption, misusing public funds, and money-laundering.
"The aim is to obtain the freezing of all Ben Ali family assets in France to avoid them being transferred to faraway locations," Sherpa spokeswoman Maude Perdriel-Vaissiere said.
Paris said at the weekend it had taken steps to block suspicious movements of Tunisian assets in France, where Ben Ali and his family are believed to have real estate holdings.
Economy Minister Christine Lagarde specified on Monday that would not entail the actual freezing of all Ben Ali's assets.
William Bourdon, Sherpa's founder and chief legal counsel, said Ben Ali's family had made considerable investments in France through opaque banking transactions.
"French authorities are perfectly aware that France is a haven for financial and banking investments, diverted for the benefit of the larger Ben Ali clan," he told RTL radio. "They are real estate investments made through a number of commercial groups and a number of banking groups, in the dark."
French government spokesman Francois Baroin told journalists on Saturday it was unclear how much Ben Ali's holdings in France were worth. The government had ordered banks to investigate and they would report their findings within days, he said.
Bourdon said he believed a trial would be complex given what he said were a group of advisers around Ben Ali who protected his financial interests, and he criticised the French government for not freezing Ben Ali's assets outright. (Reporting by Gerard Bon, writing by Nick Vinocur; editing by Noah Barkin)