Eleven of Kuwait's 21 tankers are being registered as American vessels so they can be given Navy protection. Kuwait also charters tankers flying the Soviet and British flags in its attempt to evade attacks Iran began last September on vessels owned by or serving the emirate.

Iran accuses Kuwait of receiving arms shipments for Iraq, its eastern neighbor at the northern end of the gulf. Iraq's ports were closed soon after the war began in September 1980.

Coast guard patrols in Fujairah ordered ships away from the 35-square-mile area after an Arab vessel reported sighting the sixth mine early yesterday.

Naval units of the two southern gulf countries, the United Arab Emirates and Oman, were searching for mines and the U.S. Navy was said to be helping farther from shore. A well-placed source in Saudi Arabia said its minesweepers also were in the area.

In Washington, the Pentagon said Iran probably planted the mines.

"We believe that it is quite likely, in fact almost certainly, the Iranians who left those mines there, presumably in hopes of placing them in front of our most recent tanker-escort group," said chief spokesman Robert Sims.