* Gabon says French inquiry would have no legitimacy
* Lawyer for Congo leader sees immunity possibility
LIBREVILLE, Nov 11 (Reuters) - Gabon's ruling party rejected as unfounded on Thursday a proposed French corruption investigation into assets held by its presidential family and the heads of two other African oil states.
A lawyer for Congo Republic President Denis Sassou Nguesso, who could also be targeted by the inquiry along with the leader of Equatorial Guinea, separately told French radio his client would claim legal immunity if the case went ahead.
France's highest court reopened the way this week for an investigation into assets held in France by ruling families of the three states, which according to a 2007 police investigation included luxury properties and stables of expensive sports cars.
It overruled a previous court ruling to throw out the case, which has threatened to strain French ties with the three oil-producing African nations.
"French justice has made itself a laughing stock for relying on such weak arguments," said the ruling PDG party of Gabonese President Ali Bongo Ondimba, whose father Omar was originally cited in the case before his death in 2009.
"What gives the French people the right to judge matters that do not concern it?" it said in a statement. "The PDG will expect those responsible for this decision to be accountable for any consequences."
At the time of the 2007 inquiry, Omar Bongo, Sassou Nguesso, and President Teodoro Obiang Nguema of Equatorial Guinea all denied any wrongdoing.
Jean-Pierre Versini-Campinchi, a lawyer for Sassou Nguesso, said his client would enjoy immunity as a foreign head of state and denied the Sassou-Nguesso family had improperly used assets to build up a real estate portfolio in Paris.
"How do you define the size of the Sassou-Nguesso family? If there are 180 of them the fact that they have got 18 properties between them is meaningless," he told French RFI radio.
Isabelle Thomas Werner, a lawyer representing Obiang, said earlier this week that Obiang's French assets amounted to "one miserable villa" west of Paris that was purchased in 1986 before the central African state became a serious oil producer.
Most of the populations of the three countries have seen little benefit from the oil money. Equatorial Guinea came 10th from bottom in anti-graft watchdog Transparency International's world ranking of efforts to stamp out corruption.
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