The Pacific: The Marianas, U.S.A.

America grew a little larger last week. The Northern Marianas, a group of Western Pacific islands (one of the best known: Tinian, where the Enola Gay took off for its atom-bomb run to Hiroshima in 1945), officially became a commonwealth of the U.S., and its 17,000 residents became U.S. citizens.

As residents of the United Nations' U.S. Trust Territory of the Pacific Islands, the Mariana islanders were long envious of their neighbors and fellow Chamorros to the south on Guam, who have been U.S. citizens since 1950. Although the Marianas voted overwhelmingly for commonwealth status in 1975, it took the U.N. until last May to approve the change, which President Reagan proclaimed Nov. 3. Other former members of the U.S. Trust Territory -- the Palau group, the Marshall Islands and the Federated States of Micronesia (Yap Island group, Kusaie, the Truk Islands and Ponape) -- opted for independence.

The Marianas are already adjusted to American ways. Governor Pedro P. Tenorio was in Honolulu last week negotiating with Washington officials for more federal aid. A State Department team was in the capital of Saipan processing applications for U.S. passports.