Flanked in a Rose Garden ceremony by U.N. Secretary General Kofi Annan, Nigerian President Olesegun Obasanjo and Cabinet members, President Bush plans this morning to announce a major U.S. contribution to a new global fund to combat AIDS, U.S. and U.N. officials said yesterday.

Bush's pledge of $200 million would make the United States the first government to commit resources to the fund, proposed by Annan at a meeting of African leaders last month. Administration officials were putting the finishing touches on the announcement yesterday, and it remained unclear where the unbudgeted money would come from, when it would be available, and what conditions would be placed on its use.

Although the money was not specifically included in Bush's fiscal 2002 budget proposal, officials said they expected it to be carved out of funds that have already been requested for next year. Bush will couple his announcement with a call for an international public-private partnership in which private business and foundations, along with other governments, will also contribute.

The administration's decision to embrace what has become this year's biggest U.N. initiative came as Congress continued to voice extreme displeasure with the international organization after the United States was voted off the Geneva-based U.N. Human Rights Commission last week. The House voted yesterday to withhold next year's U.N. dues unless the seat is regained.

Administration officials described the vote as unfortunate, but said it did not undermine the decision to forge ahead with an announcement timed to coincide with Obasanjo's previously scheduled visit. More than 70 percent of the 36 million people infected worldwide with HIV, the human immunodeficiency virus that causes AIDS, live in sub-Saharan Africa.

Annan, who had traveled to Washington on AIDS matters once this week, was asked to come back to appear with Bush today. In his speech to African leaders in Nigeria last month, Annan called for global expenditures of $7 billion to 10 billion a year for prevention and treatment of HIV/AIDS and other infectious diseases.

International spending on AIDS in Africa was less than $1 billion last year. To make up the difference, Annan asked wealthy governments and private donors to step up their existing programs, and to provide new money to the global fund. Details of how the fund would work and who would administer it have yet to be finalized.

As word of the pending announcement circulated among AIDS activists and nongovernmental groups, many criticized the amount as far too little. "They left out a zero," Oxfam American President Raymond C. Offenheiser said of the $200 million. The Health GAP Coalition of activist groups called it "less than a drop in the bucket . . . less than 1 percent of the proposed $1.35 trillion tax cut that will largely benefit the richest citizens of the richest nation in the world."

Others worried that the money to pay for the pledge would come out of U.S. development assistance funds, which have declined sharply over the past decade. "If the money in the end is going to come out of some other poverty funds, that's unacceptable," said David Beckmann of Bread for the World.

Mark Malloch Brown, administrator of the United Nations Development Program, praised the administration's effort, but noted that "for us in the U.N. it's absolutely critical that this is additional resources, not extracted from elsewhere in the U.S. development assistance budget."

The $200 million mirrors a figure adopted as part of the nonbinding congressional budget resolution this week. It was suggested by Sen. Bill Frist (R-Tenn.), a physician who heads the African affairs subcommittee of the Senate Foreign Relations Committee. In contrast to a 10 percent increase in this year's $460 million expenditures on international AIDS programs requested by Secretary of State Colin L. Powell, Frist proposed a $200 million increase next year, followed by an additional $500 million each year after that. Frist, who is close to Bush, has heavily lobbied the president on the issue, and has been invited to today's ceremony.

The White House was stung by criticism early this year from AIDS activists and others that it was insufficiently committed to the international fight against the disease, particularly after a frenzy of AIDS activity during the final two years of the Clinton administration. Scott Evertz, head of the Wisconsin chapter of the Log Cabin Republicans, a group of gay and lesbian party members, was named director of the White House Office on AIDS Policy last month. But State Department and Department of Health and Human Services staffers who were to be seconded to Evertz have yet to be named.

The White House has not yet decided whether to extend the mandate of a Clinton-era, 35-member Presidential Advisory Council on HIV/AIDS that expires in July. A new interagency task force on AIDS, headed by Powell and HHS Secretary Tommy G. Thompson, has yet to formally meet, although the two have held numerous conversations on the subject, including sitting down together with Annan on Wednesday.

Both Powell and Thompson have spoken repeatedly of their concern about AIDS, with Powell expressing particular worry about Africa and the Caribbean, where infection rates are also high. "Nations will collapse if we don't fix these problems," Powell said yesterday at a House subcommittee hearing on the State Department's budget proposal. Officials also said yesterday that Powell would make a trip to Africa later this month.

But pressure to take an even larger international role has increased as major pharmaceutical companies have cut their prices for sophisticated anti-retroviral AIDS drugs to the developing world. Annan said he hoped to have firm commitments for the global fund -- and an administrative structure for it established -- by late June, when the United Nations will hold a Special General Assembly on AIDS.

Comments on a General Assembly draft declaration have reflected deep disagreements over issues such as whether to buy the drugs for Africa, even at reduced prices, or whether more emphasis should be placed on HIV prevention efforts than on still-expensive treatments for those who have the disease. In its comments on the draft, the administration asked for an increased emphasis on prevention -- including mentions of sexual abstinence -- and protection of pharmaceutical intellectual property rights.