White House and GOP congressional negotiators last night ended their stalemate over the payment of nearly $1 billion in back dues to the United Nations, with the administration signaling it would accept Republican language linking the dues payments to restrictions on abortion advocacy while retaining the power to waive those restrictions.

The negotiators met in the office of House Speaker J. Dennis Hastert (R-Ill.) to work through a tentative agreement, which could clear the way for congressional approval this week of a final budget deal. The two sides already worked out most of their differences over education, police and environmental issues and added $5.2 billion that had been sought by President Clinton.

But until now they were stymied over the U.N. dues issue and Republican insistence that it be linked to restrictions on the degree to which foreign family planning groups receiving U.S. aid may spend those funds to promote abortion abroad.

Hastert returned to the Capitol late last night to help conclude the talks. He said he spoke with Clinton late Saturday and "I thought we had a tentative agreement, but the devil's in the details. . . . I think things are moving along."

A congressional aide close to the talks said: "It would surprise me if it can't be worked out. I think [the compromise] is quite reasonable. We've tried to be reasonable and the White House has also tried to be cooperative."

A White House official described the meeting as "a significant step" but said "there's more to do on the U.N. and other important issues."

As part of the compromise, the White House would accept language written into the spending legislation that would formally bar those foreign groups receiving U.S. aid from performing abortions or advocating liberalized abortion laws, according to sources familiar with the talks.

The United States has barred direct financing for abortions since 1973, but in 1984 President Ronald Reagan issued an executive order that denied grants to international family planning organizations for any purpose if they promoted abortion rights. Clinton reversed that order in 1993 shortly after taking office, but ever since Republicans led by Rep. Christopher H. Smith (N.J.) have sought to write Reagan's executive order into law, which this compromise would accomplish.

But in return for accepting the abortion language, Clinton would have the option of waiving the law if he saw fit. However, a waiver would automatically result in about a 3 percent cut in the $385 million international family assistance funding, a $12.5 million penalty.

As part of the deal, the Republicans would also go along with the administration's proposal for expanding the International Monetary Fund's debt relief and forgiveness efforts through the sale or revaluing of some of the gold held by the multinational lending institution. The White House said last night that the details of the IMF understanding still must be worked out.

In addition to Hastert, Clinton conferred by phone with Senate Majority Leader Trent Lott (R-Miss.) and congressional Democratic leaders over the weekend from the White House and en route to Turkey yesterday.

If the tentative agreement holds up, it would mark an important victory for Republicans, who found a way to advance their antiabortion policy without appearing to have blocked efforts to end the embarrassing spectacle of the government as a U.N. deadbeat. Both the administration and GOP leaders are sensitive to the fact that unless the U.N. arrearage controversy is settled before Congress adjourns, the United States would lose its vote in the United Nations General Assembly--but not in the more powerful Security Council. Clinton and other White House officials recently signaled a willingness to agree on some restrictions on foreign family planning groups, but the administration was concerned about alienating congressional Democrats and women's groups that support abortion rights. Moreover, advocates of international population control efforts argue that the Republicans are attempting to trample on their rights to free speech and to provide health services that affect women's lives.

However, sources familiar with the White House's thinking note that the restrictions would not be permanent but would be written into a fiscal 2000 spending bill that will expire 10 months from now. And the sources said there can be little doubt that Clinton will use the waiver.

Yesterday, Senate Minority Leader Thomas A. Daschle (D-S.D.) voiced confidence that a final agreement would come this week, adding, "We simply cannot tell the world that we're going to shrink from our responsibilities at the United Nations" because of a political dispute over abortion.

Daschle referred to the emerging deal during an appearance on CBS's "Face the Nation" but raised some doubt about whether the compromise would be fully acceptable to the two sides. "I'm not even sure that would work," Daschle said.

Meanwhile, new government figures showing that Medicare spending declined slightly last year, for the first time ever, are likely to provide added impetus for congressional action this week to restore $11 billion of cuts in the program that many hospitals and health care providers say have caused them hardship.

Medicare spending for the elderly and disabled was growing at a rate of 10 percent annually when Congress curbed payments in the 1997 balanced budget deal. More recently, however, Medicare spending has dropped far more than lawmakers and experts had anticipated. New Treasury figures indicate that expenditures declined by less than a percentage point, from $213.6 billion in 1998 to $212 billion in the fiscal 1999, which ended Sept. 30.

While the unprecedented spending decline may prove to be an anomaly, White House officials and budget experts said the new figures strengthen the argument that the cuts in Medicare went too far.

"These numbers provide validation that the steps we are taking to moderate the impact of [cuts] on health care providers are warranted," said Chris Jennings, a White House health policy adviser.

CAPTION: Senate Minority Leader Thomas A. Daschle pushed for compromise.