The Bush administration’s plan to expand fossil fuel exploration in the West ran into an obstacle Wednesday when a federal judge temporarily blocked the Interior Department from allowing energy prospecting on thousands of acres of public land in Utah. The ruling halted a project by a seismic exploration company to search for oil and gas reserves in Utah’s Arches National Park. The company intends to use 60,000-pound “thumper trucks” to vibrate the ground to test for oil deposits. Environmentalists say such testing would cause irreparable harm to the area and are asking the court to require the feds to conduct an environmental impact study before allowing the exploration to continue. The Interior Department believes no such study is necessary. A similar dispute is brewing over an oil and gas exploration project near Utah’s Dinosaur National Monument.