The suit seeks to compel the US military to identify toxic wastes it supposedly left behind in its former Philippine facilities.
"If the extension is granted, we expect a ruling on the suit by the first week of April," said lawyer-activist Cora Fabros, who helped put up the case.
"We’re waiting for word from our American counterparts," added Fabros, a top officer of the People’s Task Force for Bases Clean-up.
The lawsuit has received the support of Greenpeace International, the Filipino American Coalition for Environmental Solutions and Arc Ecology.
It was filed under the provisions of the American Comprehensive Environmental Response, Compensation and Liability Act, better known as the Superfund Law.
"This suit is being brought under the citizen suit provision of the law," said American lawyer Scott Allen in a statement last December.
While the lawsuit does not seek compensation, it would, if granted, support a civil case, which Clark and Subic residents filed in a local court two years ago, according to Angeles City-based lawyer Alex Lacson.
When the US military abandoned Subic and Clark in 1992, environmentalists claimed it left behind toxic wastes, blamed for ailments afflicting a number of residents around the former US facilities.