New York State's highest court yesterday gave New York City at least six more months to pay off much of nearly $1 billion in due debts the court has said the city eventually must repay.

The Court of APpeals, which ruled in November that a state-imposed moratorium on these debts was unconstitutional, granted the city's request to turn the matter back to a lower court for decisions on details of the repayment.

That guaranteed the city at least some delay in repayment-time which the city has said it needs to try to negotiate a plan for raising the $1 billion from other sources.

And the court ruled that when the matter does get back to the lower court, only a small part of the $1 billion must be paid immediately. That immediate repayment involves some $550,000 in the city's short-term notes held by Flushing National Bank, which brought the suit that generated the November ruling.

The lower court was directed to get Flusing paid off within 30 days after the bank flies a final application with it for the money, and to see that the city pays off any individual citizens who hold the notes involved withing a similar 30-day period after they apply for their money.

But the Court of Appeals said the lower court may take as long as six months in arranging for repayment of "institutional or corporate holders" of the notes. There are no reliable figures on how large a proportion of the $983 million in notes frozen by the moratorium are held by such large investors.