People with H.I.V. should be put on antiretroviral drugs as soon as they learn they are infected, federal health officials said Wednesday as they announced that they were halting the largest ever clinical trial of early treatment because its benefits were already so clear.

The study was stopped more than a year early because preliminary data already showed that those who got treatment immediately were 53 percent less likely to die during the trial or develop AIDS or a serious illness than those who waited.

The study is strong evidence that early treatment saves more lives, the officials said. Fewer than 14 million of the estimated 35 million people infected with H.I.V. around the world are on treatment now, according to U.N.AIDS, the United Nations AIDS-fighting agency. In the United States, only about 450,000 of the estimated 1.2 million with H.I.V. are on treatment, according to the Centers for Disease Control and Prevention.

“This is another incentive to seek out testing and start therapy early, because you will benefit,” said Dr. Anthony S. Fauci, director of the National Institute for Allergy and Infectious Disease, which sponsored the trial. “The sooner, the better.”