The Supreme Court ensured Monday that trial of a lawsuit involving U.S. passengers of the Achille Lauro, the Mediterranean cruise ship hijacked by terrorists in October 1985, will be held in the United States.

In a unanimous ruling, the court affirmed a 2nd U.S. Circuit Court of Appeals ruling, which said it was premature for the ship owner to appeal a trial court ruling refusing to dimiss a suit filed by the Americans.The ruling assures at least a trial on the merits of the case in U.S. courts and not in Italian courts as owners of the cruise ship had sought. However, if later rulings determine the case should have been heard in Italy, any American judgment can be reversed.

At issue in the case was whether the damage suit should be tried in the United States or Italy, where Lauro Lines is based.

The lawsuit was filed in federal court in New York by passengers who were aboard the Achille Lauro when it was hijacked, and by the children of Leon and Marilyn Klinghoffer. The suit seeks damages for physical and psychological injuries and for the wrongful death of Leon Klinghoffer.

He was shot dead and thrown overboard during the incident, and his wife has since died.

The district court refused to dismiss the suit and, on appeal, the 2nd Circuit said the issue could not properly be considered until after the litigation has run its course.

In other action, the court:

-Agreed to decide if the government must deal separately with overpayments and underpayments to Social Security beneficaries. The case deals with a complex system used by Social Security to handle erroneous payments. Under the system, when an error, whether an over or underpayment, is discovered the agency reviews all payments to the person to determine how long the error went on and whether it was offset by other errors.

-Let stand a ruling that orders to trial a "brainwashing" suit brought against the Unification Church of the Rev. Sun Myung Moon. The court refused to hear the case brought by the church seeking review of a ruling by the California Supreme Court that ordered the case to trial.

-Upheld a lower court ruling in a 6-3 decision on Green vs. Bock Laundry Machine Co. of Lemoyne, Pa., that a judge may allow defendants to introduce evidence of a plaintiff witness's prior felony convictions in a civil case.