Now that the White House and congressional Republicans have struck a deal to pay $926 million to the United Nations, U.S. Ambassador Richard C. Holbrooke is launching a campaign to persuade the organization's 187 other members to accept that sum as full payment of all U.S. debts to the world body.

It will be a hard sell. By the United Nations' calculation, the United States owes $1.52 billion in annual dues and assessments for peacekeeping operations dating to the early 1990s. As many diplomats here see it, there is no reason to give the world's richest country a $600 million discount.

Congress's willingness to provide the $926 million, however, is contingent on a long list of conditions, including the world body's acceptance of it as full payment, a permanent cut in the American share of U.N. expenses and a firm pledge that the U.N. administrative budget will not rise for the next two years.

In an interview today, Holbrooke said he will ask the developed nations of Europe, as well as countries with fast-growing economies, such as China, to increase their portion of U.N. finances. He added that he has invited delegates from key countries to a reception Wednesday for Donald S. Hays, the new U.S. representative to the United Nations for reform and management, to explain why it is in their long-term interest to shoulder more of the burden.

Meanwhile, he said, Secretary of State Madeleine K. Albright will lobby their bosses around the world.

"This is not a diktat from Washington, this is an effort at persuasion," Holbrooke said. "It will take a long time, it won't be easy, and we will go from country to country, from Argentina all the way to Zimbabwe.

"I will be doing this in New York, and Madeleine will be doing it in capitals," he added. "It will be a very heavy hit."

The United States wants to reduce its share of the regular U.N. operating budget to 22 percent, from the current 25 percent. Holbrooke estimated that the reduction would amount to about $35 million a year.

In addition, the United States is seeking to lower its special assessment for U.N. peacekeeping operations to 25 percent, from the current 31 percent. Those costs vary enormously from year to year.

"Several countries have indicated that their governments will make the increase," Holbrooke said. "Others have said, 'We don't want to see you.' "

To win congressional approval for the U.S. payment, the Clinton administration reluctantly agreed to language attached by Rep. Christopher H. Smith (R-N.J.) banning U.S. aid to international family planning organizations that promote abortion rights. A major impetus for the compromise was that the United States will lose its seat in the U.N. General Assembly--though not in the more powerful Security Council--if it does not pay at least $350 million of its debts by Jan. 1.

The congressional spending bill authorizes an initial payment of $100 million before the end of the year. But a U.S. official said the administration can make up the difference with "a little creative accounting."

The administration probably will borrow $204 million from a payment earmarked for current U.S. dues, and could borrow the rest from funds intended to pay for a U.N. war crimes tribunal and current U.N. peacekeeping operations, the official said.

Holbrooke will face an even trickier problem next month when the General Assembly begins consideration of the world body's 2000-01 budget. In May, U.N. Secretary General Kofi Annan proposed an increase of $120 million, from $2.535 billion to more than $2.65 billion, over the next two years. If Holbrooke is unable to block that increase, the legislation will force the Clinton administration to withhold 20 percent of U.S. funding for the United Nations in 1999.

U.N. diplomats said that Holbrooke needs to lobby members of the Group of 77, a coalition of Third World countries that oppose a budget cap. "I hope the U.S. has a plan on how to sell this," said one U.N. diplomat. "Everybody's eyes are on Holbrooke and his famous skill as a salesman of hard choices."

CAPTION: Ambassador Richard C. Holbrooke, shown at a Senate hearing in 1996, will try to persuade the United Nations to accept a reduced U.S. debt payment.