U.S. President George W. Bush's sudden commitment to fight AIDS in the world's poorest countries drew sustained applause in Congress, but Stephen Lewis says the vow is only a first step.

"This is a signal that the United States has decided to respond to the pandemic much more seriously than it has before," he said. "It is a signal that will alert the world to do the same."

Mr. Lewis, the Canadian political veteran who serves as United Nations special envoy on HIV-AIDS in Africa, said he is encouraged by the $15-billion (U.S.) pledge but will wait to see how the money would be delivered before he becomes excited.

He said that large promises have been made in the past, but far less comes from them.

He wants to ensure that the commitment is not forgotten, especially in light of the growing possibility of a U.S.-led war on Iraq.

"The promise has been made, the assurance has been given; we have to make sure this happens," he said Tuesday night from Johannesburg, where he is studying the links between famine and AIDS.

When it was established, the global fund to fight AIDS, which Mr. Lewis called the "strongest vehicle for treatment and prevention," had a commitment from Western countries of $2-billion.

Mr. Lewis said he believes that the best outcome of the announcement would be pressure on the other most-developed countries to make contributions toward the treatment of AIDS in Africa. "The whole purpose of the last year has been a drum roll of desperation to get money from Western donors. This, at least, opens the door."

He expects all nations in the Group of Seven to have pledged similar contributions by their June meeting in France, he said.

"Countries like Canada are really on the hook to go back to their own treasuries and ask how they are going to up their own contributions to the epidemic," he said. "I don't know how they can escape it."

In his address, Mr. Bush said he would "ask Congress to commit $15-billion over the next five years, including nearly $10-billion in new money, to turn the tide against AIDS in the most afflicted nations of Africa and the Caribbean."

The White House said the plan would target Botswana, Ivory Coast, Ethiopia, Kenya, Mozambique, Namibia, Nigeria, Rwanda, South Africa, Tanzania, Uganda and Zambia, in Africa, and Guyana and Haiti.

Pointing to the dropping costs of treatment, Mr. Bush called on Congress to help provide care for millions of people suffering from AIDS. "Seldom has history offered a greater opportunity to do so much for so many."

He said the money should prevent seven million new AIDS infections and treat at least two million people with life-extending drugs.

To highlight the plan, he had invited Peter Mugyenyi, a Ugandan scientist at the forefront of the AIDS battle, to attend the speech. Dr. Mugyenyi was present in the visitors' gallery, seated next to U.S. first lady Laura Bush.

Mr. Lewis said that of the 30 million people estimated to be infected with HIV in Africa, three million to five million require immediate care.

Last year, UN Secretary-General Kofi Annan said that $10-billion a year is needed to fight AIDS in Africa.