With the stakes higher than ever, President Clinton and Republican conservatives on Capitol Hill are locked again in a long-festering dispute over abortion that is holding up payment of nearly $1 billion owed by the United States to the United Nations.

Although the fight has been going on for three years, it has a greater sense of urgency this year because the United States is threatened with the loss of its vote in the U.N. General Assembly if payment is not made by the start of the year.

Under the U.N. Charter, a nation automatically loses its vote in the 188-member assembly--but not the more powerful and exclusive Security Council--if it falls more than two years behind in its payments, which the United States would do as of Jan. 1, according to U.S. and U.N. officials.

The dispute arises out of a deal cut by key senators in 1997 to pay back dues and assessments in exchange for budgetary reforms, including a reduction in the U.S. share of the U.N. budget. But House Republicans demanded that payment of the debt be conditioned on Clinton's acceptance of legislative language banning U.S. assistance to international family planning organizations that lobby foreign governments to liberalize their abortion laws.

Clinton refused to go along with the demands in 1997 and 1998 and recently cited this "unacceptable linkage" as one of his reasons for vetoing the appropriations bill that included this year's installment of the U.N. payment.

With time drawing short as Congress prepares to adjourn for the year, the administration and GOP leaders are blaming each other for intransigence and ratcheting up the rhetorical pressure for concessions that neither side has been willing to make in the past. Key lawmakers said there is a chance, although a slim one, that a breakthrough can be reached to ensure the payment before Congress leaves town sometime next month.

At the White House and at U.N. headquarters in New York, Clinton and Richard C. Holbrooke, U.S. ambassador to the world body, have been beating the drum for action by Congress to make the payment without conditions, including some technical matters that also could threaten this country's General Assembly vote.

On Monday, Clinton said approval of the U.N. funding was essential to America's ability to fulfill its international obligations and thus a matter of "national security." Yesterday Holbrooke was personally lobbying on Capitol Hill for the money, as he has done once or twice a week for several weeks.

"The family planning issue is not a national security matter" and should not be treated as such by being combined with U.N. funding, Holbrooke said during a brief interview. "If we lose the [General Assembly] seat, we lose a lot more than that. We lose our international standing," he added.

But Senate Majority Leader Trent Lott (R-Miss.) said Tuesday that Clinton must accept at least some abortion restrictions to get the U.N. funding. "They're going to have to just face up to the realization that, in order to get the U.N. arrearages, they're going to have to agree to some limits on using federal taxpayers' dollars to promote abortions around the world," Lott said. He called on Clinton to designate someone from the administration to work on the family planning dispute.

The Senate earlier this year approved the U.N. funding without any abortion restrictions as part of a State Department authorization bill for the year. The House avoided both subjects in its version of the legislation, leaving the issue to be resolved in a House-Senate conference. But House leaders have not appointed conferees, giving rise to speculation by Democrats and some Republicans that the abortion dispute will become a bargaining chip in end-of-the-session negotiations over spending and other key issues.