(FORTUNE Magazine) – -- While the U.S. Navy is providing escorts for Kuwaiti oil tankers plying the Persian Gulf, it is doing nothing to protect American-owned carriers. That's because most ships do not fly U.S. flags to avoid paying American crews wages two to three times more than foreign sailors'. Kuwaiti vessels also have foreign crews. But a loophole in U.S. law allows them to display the Stars and Stripes. Defense Department policy is ''Protection follows the flag.'' Now American shipowners are worried because at least four U.S.-owned supertankers have been hit in the Gulf. Chevron and Loews' Majestic Shipping subsidiary are mobilizing in Washington to get protection, and Exxon, Mobil, and Texaco are quietly supporting the effort. Says Loews Executive Vice President James Tisch: ''Even though we don't fly American flags, our ships are part of the U.S. reserve fleet. In case of national emergency, they are subject to U.S. income tax, and they are inspected and regulated by the Coast Guard.'' Capitol Hill sources think the White House has not acted because it fears that Congress might exploit such a move to invoke the War Powers Act, which gives legislators a say in the use of U.S. military forces overseas. Back in the Gulf, meanwhile, captains of the behemoth oil tankers are tagging along behind U.S. Navy convoys. One captain recently guessed wrong about a convoy's destination and steamed into an Abu Dhabi dry dock.