The administration, Carmona said Tuesday, would not allow him to speak or issue reports on the subjects of stem cells, emergency contraception, sex education or prison, mental or global health issues. Top officials tried to "water down" a landmark report on secondhand smoke and delayed it for years, he said. Released last year, the report concluded that even brief exposure to cigarette smoke can cause immediate harm.

Carmona said he was ordered to mention President George W. Bush three times on every page of his speeches. He also said he was asked to make speeches to support Republican political candidates and to attend political briefings.

Administration officials even discouraged him from attending the Special Olympics because, he said, of that charitable organization's longtime ties to a "prominent family" that he declined to name. "I was specifically told by a senior person, 'Why would you want to help those people?' " Carmona said.

The Special Olympics is one of the nation's premier charitable organizations to benefit disabled people, and the Kennedy family has long been deeply involved in it. When asked after the hearing whether that "prominent family" was the Kennedys, Carmona responded, "You said it. I didn't."

Basically, Adjudin nips wannabe sperm cells in the bud. Those cells, called germ cells, ordinarily develop into sperm. But they need the help of other cells, called Sertoli cells, to reach that destiny.

Adjudin interferes with the process.

Cheng's team previously reported from other animal tests that Adjudin, given orally by itself, was too toxic to be a suitable contraceptive because it caused liver inflammation and muscle shrinkage (atrophy).

So the scientists bundled Adjudin with a synthetic version of the sex hormone FSH (follicle-stimulating hormone) and injected it into the bellies of four male rats.

"At the moment, the government of Uganda appears to be under the influence of the American policy through the presidential initiative of emphasising abstinence far and away over condoms," he said.

He suggested US President George Bush, who launched his multi-billion dollar campaign to tackle Aids in Africa two years ago, was acting under the influence of the religious right in US.

A senior US official rejected Mr Lewis's criticism, saying the current administration supported condom use as part of a balanced programme that included prevention.

"The statements that I have heard are completely untrue and completely mischaracterise effective prevention programmes," Mark Dybul, deputy US global Aids co-ordinator told Reuters news agency.