The World Health Organization on Friday forcefully endorsed wider use of the insecticide DDT across Africa to exterminate and repel the mosquitoes that cause malaria. The disease kills more than a million people a year, 800,000 of them young children in Africa.

Dr. Arata Kochi, who leads the group's global malaria program, unequivocally declared at a news conference on Friday that DDT was the most effective insecticide against malaria and that it posed no health risk when sprayed in small amounts on the inner walls of people's homes. Expanding its use is essential to reviving the flagging international campaign to control the disease, he said.

Dr. Kochi has powerful allies on DDT and, more broadly, on using insecticide sprays, in Congress and the Bush administration - an odd bedfellows coalition for an agency of the United Nations, which has often been at odds with the White House.

At the news conference, Adm. R. Timothy Ziemer, who leads President Bush's $1.2 billion malaria undertaking, stood at Dr. Kochi's side and described spraying with insecticides as a tool "that must be deployed as robustly and strategically as possible."

The health organization's news release quoted Senator Tom Coburn, Republican of Oklahoma.

"Finally, with the W.H.O.'s unambiguous leadership on the issue, we can put to rest the junk science and myths that have provided aid and comfort to the real enemy - mosquitoes," said the senator, a medical doctor.

Dr. Kochi said the most substantive change in the W.H.O.'s guidelines on the use of insecticides would extend the reach of the strategy. Until now, the agency had recommended indoor spraying of insecticides in areas of seasonal or episodic transmission of malaria, but it now also advocates it where continuous, intense transmission of the disease causes the most deaths.

Dr. Kochi's new policies and abrasive style have stirred the small world of malaria experts. Dr. Allan Schapira, a senior member of the W.H.O. malaria team who most recently oversaw its approach to insecticide spraying, resigned last week.

Reached Thursday on his cellphone, Dr. Schapira declined to comment on his reasons, except to say that they were professional. He did not return messages left Friday.

His successor, Pierre Guillet, a medical entomologist, said Dr. Schapira quit because he was uncomfortable with the new approach on insecticide spraying.

There are fierce debates among experts over when it is best to use indoor spraying or mosquito nets impregnated with insecticides that last up to five years, though most agree that both spraying and nets are important tools.

Dr. Kochi said in an interview that half the professional staff of the W.H.O.'s malaria program has left "one way or the other" since he took over in October. He described Dr. Schapira as the "main brain" behind the past approach.

"He was professionally insulted by me," Dr. Kochi said.

In answer to a question, Dr. Kochi acknowledged that he had indeed told members of the staff in meetings that they were stupid. "They are very inward looking, and they do not communicate outside the malaria field," he said. "It's ridiculous."

Dr. Kochi earlier headed the W.H.O.'s tuberculosis campaign until he was forced out after his blunt manner alienated important partner organizations.

He has brought the same in-your-face approach to malaria. In January, he demanded that 18 drug companies - all named - stop selling some forms of a new malaria drug he believed could speed up drug resistance. If they did not comply, he threatened to try to disrupt sales of their other medicines.

In April, he accused the Global Fund to Fight AIDS, Tuberculosis and Malaria, through which rich countries finance health campaigns, of ignoring W.H.O. rules that forbid treating malaria with herbal-based therapy alone - a charge that Dr. Bernard Nahlen, a senior adviser at the Global Fund, called "outlandish" on Friday.

There are now 17 African countries using at least some indoor spraying of insecticides to combat malaria. Only 10 of them use DDT - Eritrea, Madagascar, Ethiopia, Swaziland, South Africa, Mauritius, Mozambique, Zimbabwe, Namibia and Zambia - the W.H.O. said. Too many countries in Africa have shied away from DDT, Dr. Kochi said, because of the nasty environmental reputation it earned in an earlier era when it was widely sprayed on crops - dangers that do not apply when spraying small amounts indoors.

DDT has carried a special stigma since the publication in 1962 of Rachel Carson's "Silent Spring," which helped set off the environmental movement in America by documenting how mass spraying of DDT entered the food chain, causing cancer and genetic damage and threatening to wipe out some bird species, including bald eagles.

The nonprofit group, Beyond Pesticides, distributed news releases on Friday opposing the W.H.O.'s new policy, saying a dependence on pesticides like DDT "causes greater long-tem problems than those that are being addressed in the short-term."

Dr. Kochi said some African countries had also been reluctant to use DDT because of fears that European countries would block food exports if crops were tainted by even minuscule amounts of DDT. In an interview, he called on leaders of the European Union to publicly encourage African countries to use DDT against malaria. Uganda, for one, has not used it because of what Dr. Kochi called "a bureaucratic standoff between the ministry of health and the ministry that oversees trade."

A spokesman for the European Union, Alain Bloedt, said Friday that it was too late in the afternoon to get a reply.

Dr. Kochi said he himself did not worry about whether he would lose his job if he took on too many influential players. Success will require many difficult changes, he said. "I don't want to fail."