The nation's dependence on foreign oil has troubled energy experts since the Arab oil embargo in 1973. Policies calling for more reliable sources of oil, curbs on energy consumption and the development of alternative fuels have reduced the dependence, but U.S. use of foreign oil still has continued to grow. Now the Sept. 11 terrorist attacks have intensified energy concerns. Some observers say the use of airliners as weapons places the entire domestic energy system at risk, including nuclear power plants and oil pipelines. But most experts agree that the biggest threat to U.S. energy security remains dependence on foreign oil. To reduce the risk, the Bush administration proposes more domestic production — including drilling in the Arctic National Wildlife Refuge — while Democrats favor conservation measures and increased use of renewable fuels.