In a powerful opening to the first global gathering on HIV/AIDS, U.N. Secretary-General Kofi Annan urged world leaders Monday to set aside moral judgments and face the unpleasant facts of a disease that has killed 22 million people and ravaged many of the world's poorest nations.

"Up to now, the world's response has not measured up to the challenge," Annan said.

The secretary-general, who has made the fight against AIDS his personal priority, said money must be urgently mobilized and used effectively in response to this "unprecedented crisis."

The United Nations opened a three-day session on AIDS with a potent symbol -- a multicolored, patchwork quilt honoring the millions of lives lost to one of the worst epidemics in human history.

Expectations for a successful gathering are high and varied for many of the 3,000 participants, including health experts, politicians, scientists, AIDS activists and patients working to find an end to the scourge.

Three days of conferences and meetings touching on everything from drug prices to homosexuality, AIDS orphans and funding, will conclude Wednesday with a document mapping out a global strategy to halt the disease and reverse its effects.

Hours before the conference, however, diplomats were still arguing over treatment versus prevention and fundamental differences on the language in the document. Many Muslim nations and even the United States are vehemently opposed to specifically naming the disease's most vulnerable groups, including homosexual men. Others argue it is imperative to identify those most in need of the world's attention in the AIDS fight.

"When we urge others to change their behavior, so as to protect themselves against infection, we must be ready to change our own behavior in the public arena," Annan told the 189-nation General Assembly.

"We cannot deal with AIDS by making moral judgments or refusing to face unpleasant facts, and still less by stigmatizing those who are infected. We can only do it by speaking clearly and plainly, both about the ways that people become infected, and about what they can to avoid infection."

Somber messages were expected to follow from the leaders of Kenya and Nigeria -- each home to more than 2 million HIV patients -- and from impoverished Botswana and Zimbabwe, where more than 20 percent of the adult population is infected, as well as South Africa, where AIDS will knock off 17 years of life expectancy by 2005.

Two dozen heads of state, mostly from Africa, are attending the General Assembly Special Session on HIV/AIDS, but no wealthy nation is sending its president or prime minister. The 40-member U.S. delegation will be represented by Secretary of State Colin Powell.

U.N. radio and an online webcast will broadcast many of the events around the world in the six official languages of the United Nations -- Arabic, Chinese, English, French, Russian and Spanish.

To allow some delegates to participate, the United States waived visa restrictions that prevent those with HIV or AIDS from visiting the country.

For days, U.N. staff have come to work with small, bow-shaped red ribbons pinned to their lapels. Two giant red AIDS ribbons were illuminated in windows on both sides of the U.N. Secretariat building.

Events on Monday alone include a round-table discussion on prevention and care, a look at how New York City has responded to the epidemic, gender issues relating to AIDS, challenges in rural Africa and the psychological impact of the disease. Canada is expected to announce a contribution to the global fund.

Annan has said $7 billion to $10 billion is needed annually to deal with the disease. So far three countries -- the United States, Britain and France -- have contributed to the fund along with three private donations, for a total of $528 million.

"Spending on the battle against AIDS in the developing world needs to rise to roughly five times its present level," Annan said Monday. Annan applauded those who have already pledged contributions. "I hope others will follow their example, during and after this special session."

On Friday, Powell expressed frustration over the trickle of donations from Europe to the AIDS fund. He also promised to ask Congress to increase the U.S. contribution.

"Everybody should be coming up on this, every European country," Powell said.

A study published Friday in the journal Science said the world's poorest countries will need $9.2 billion a year to deal with AIDS -- $4.4 billion to treat people with the illness and $4.8 billion to prevent new infections.