To achieve the deal, the Clinton administration will have to placate anti-abortion sentiment in the Republican Party.

Long hostile to many aspects of the UN, Republicans have focused on the international organisation's support of pro-abortion agencies.

Abortion is an emotive political issue in the US

The United States is the largest contributor to the United Nations but also its largest debtor, owing about $1.7bn, according to UN figures.

However, Washington puts the amount at closer to $1bn.

The budget agreement would release $926m over a period of three years for the payment of UN dues.

Republicans look likely to agree to the deal, because its wording will cut off US financing for international organisations that promote abortion rights, and which are funded through the UN.

The deal would reduce the amount of money which the US Administration spends on such organisations, currently around $385m a year.

However, in a victory for the White House, the reduction could be as little as $10m a year and will apply only to this year's budget appropriations.

House Republicans had sought to make the reduction permanent and much larger.

A deal on the UN dues is one of the last remaining obstacles to a deal between the White House and Congress on the budget for the fiscal year 2000, which began on 1 October.

Emergency funding measures have kept the US Government running since then.

Deadline

If the United States does not make an instalment payment of at least $550m by 31 December, it will lose its vote in the UN General Assembly.

Failure to pay would not jeopardise the US General Assembly seat or its vote on the UN Security Council.

UN ambassadors have welcomed signs of a breakthrough, but not without reservations over its timing and conditions.

Canadian Ambassador Robert Fowler said his government had "severe problems" with the deal because it would not pay all the arrears.

UK Ambassador Greenstock: Still some resistance ahead at the UN

But he said if it meant that in the short term that the US did not lose its vote in the General Assembly, it was good news.

UK Ambassador Jeremy Greenstock said there was still concern about continued Senate demands for settling the US bills.

The original legislation for the payment included a large number of conditions, including demands that the US share of the regular UN budget be reduced from the present 25% to 20%, and that its share of peacekeeping operations be reduced from 31% to 25%.

US Ambassador to the UN Richard Holbrooke indicated to the council these conditions would be part of the package.

"That has still got to go through the UN membership and there would be some resistance to that package as it stands," Mr Greenstock said.