The Supreme Court on Tuesday imperiled a law that treats fathers and mothers differently in deciding whether their children born out of wedlock and outside the country are U.S. citizens.

That result came about even as the court voted 6-3 to reject a sexual-equality challenge to the immigration law that automatically deems such children citizens if their mother is American, but requires more if only their father is American.Two justices who voted to uphold the law in today's decision indicated they believed it could be successfully challenged. If so, that would result in a 5-4 ruling against treating the parents differently.

The court's rationale was splintered. The six-justice majority wrote three separate opinions that cited three separate and distinct reasons for the ruling.

In a separate case, the justices gave federal courts the power to resolve competing ownership claims by states and treasure hunters. That ruling came in a dispute over a Gold Rush-era ship that sank off California's coast 133 years ago.

The citizenship law had been challenged by Lorelyn Penero Mil-ler, who was born in 1970 in the Philippines. Her mother was a Filipino and her father a U.S. serviceman stationed there. Her parents were not married.

Federal law says such children can be deemed U.S. citizens if one of three things occur before their 18th birthday:

-The child is legitimated through its parents' marriage.

-The father acknowledges paternity in writing under oath.

-Or paternity is established in court.

People seeking citizenship this way used to have until age 21. Several months after her 21st birthday, Miller applied to the State Department for U.S. citizenship. Her request was denied because her father had not established paternity before her 21st birthday.

In 1992, while Miller was living with her father in Tyler, Texas, he filed in a state court a sworn acknowledgment of his paternity. Miller sued after the State Department refused to reconsider her application for citizenship.

A federal trial judge and a federal appeals court rejected her lawsuit, relying heavily on a 1977 Supreme Court decision that said Congress has exceedingly broad discretion to determine which people born outside the United States are citizens.

Today, the Supreme Court said the lower courts were right to dismiss Miller's lawsuit.

Justice John Paul Stevens wrote for himself and Chief Justice William H. Rehnquist that the differing treatment does not violate men's equal-protection rights.

"The biological differences between single men and single women provide a relevant basis for differing rules governing their ability to confer citizenship on children born in foreign lands."