By Lawrence Hurley

WASHINGTON (Reuters) - The Supreme Court on Monday left in place a lower-court ruling preserving American Samoa's status as the only overseas U.S. territory without birthright U.S. citizenship, rejecting a legal challenge aimed at making people born there automatic citizens.

The justices declined to hear an appeal of a 2015 ruling by the U.S. Court of Appeals for the District of Columbia Circuit that went against five American Samoans led by Leneuoti Tuaua arguing for birthright citizenship.

The Obama administration and the U.S. South Pacific territory's government favor keeping the status quo.

The people of American Samoa are considered noncitizen U.S. nationals, a status that denies them the full rights of American citizenship. The territory has a population of roughly 55,000.

The appeals court held that the "citizenship clause" of the U.S. Constitution's 14th Amendment does not automatically extend to unincorporated U.S. territories like American Samoa. The clause holds that "all persons born ... in the United States, and subject to the jurisdiction thereof, are citizens of the United States."

American Samoa has been a U.S. territory since 1900. The U.S. Congress previously has decided on a territory-by-territory basis whether people born in the various overseas territories including Puerto Rico, Guam, the U.S. Virgin Islands and the Northern Mariana Islands automatically become U.S. citizens. American Samoa was the only one denied birthright citizenship.

Citizenship would make the plaintiffs eligible for full U.S. passports and such rights as being able to vote in national elections if they reside in a U.S. state. Currently, American Samoans can obtain U.S. passports with an imprint describing them as noncitizen U.S. nationals.

The government of American Samoa argues opposes birthright citizenship, saying in court papers that unique Samoan cultural traditions "might be threatened by a fundamental change in the status of the American Samoan people." The territory's leaders said that "whether birthright citizenship should extend to the people of American Samoa is a question for the people of American Samoa and its elected representatives, and not for this (Supreme) Court to decide."

Those born in the territory can claim citizenship if, at birth, one of their parents was a U.S. citizen. They can also pursue naturalized U.S. citizenship, but the lawsuit said they should not need to go through that "lengthy, costly and burdensome" process.

(Reporting by Lawrence Hurley; Editing by Will Dunham)