After a decade of court battles, lawyers this week took a lawsuit by Ecuadorean Indians accusing U.S. oil firm ChevronTexaco Inc. of polluting the Amazon jungle into the field. Scientists started taking soil samples from the Amazon, hoping to prove, or disprove, that a Texaco subsidiary contaminated groundwater supplies during its oil operations in Ecuador from 1972 to 1992. The tests near the sweltering jungle town of La Joya de los Sachas marked the beginning of six months of inspections that plaintiffs and defendants believe will be definitive.