Chevron Corp said it had filed an international arbitration claim against Ecuador, opening a new front in its defense against a $27 billion environmental damage lawsuit in Ecuadorean court…Claiming Ecuador's government has violated a bilateral U.S.-Ecuador investment treaty, Chevron said…an arbitration proceeding had commenced before the Permanent Court of Arbitration in The Hague under United Nations trade law…Chevron says that in 1998, Ecuador and state oil company Petroecuador released Texaco from further liability after Texaco's remediation work was completed. But plaintiffs in the case argue that the release did not deal with private claims against the company.