The Food and Drug Administration is delaying by three months a decision on whether to approve a drug for preventing infection with HIV, the virus that causes AIDS.

An agency decision on the drug Truvada, made by Gilead Sciences, was expected by June 15. But the decision was pushed back to give the agency time to review a new Gilead plan to limit the risks to healthy people taking the drug, Cara Miller, a company spokeswoman, said Friday.

If approved, Truvada would become the first drug marketed for prevention of HIV. The FDA will now make a decision by Sept. 14.

In May, a committee of FDA advisers recommended that the agency approve Truvada for HIV prevention in specific high-risk groups, including men who have sex with men and partners of those infected with HIV.

After that meeting, the FDA asked Gilead to revise its risk-management plan for the drug, Miller said.

She declined to provide details on how Gilead revised this plan, which is known as a risk evaluation and management strategy.

During the May meeting, FDA advisers wrestled with safety concerns, including fears that men taking the drug would see it as an excuse to stop using condoms, and worries that healthy people would not take the drug daily as prescribed.

The biggest safety worry: that people already diagnosed with HIV will take the drug, a scenario that can trigger drug-resistant, difficult-to-treat HIV.

An HIV-testing plan to ensure that those given Truvada are negative for the virus is “pivotal,” said Mitchell Warren, executive director of AVAC, an AIDS advocacy group.

“Gilead has said they will provide free HIV testing” to potential Truvada takers, said Warren. “That’s terrific. Hopefully the back-and-forth between Gilead and FDA will provide more clarity on how they’ll do that.”

Interim guidelines for use of Truvada from the Centers for Disease Control and Prevention indicate that anyone interested in using the drug for prevention first must be tested for HIV.

Michael Weinstein, president of the AIDS Healthcare Foundation, an advocacy group that opposes approval of Truvada for prevention, applauded the delay.

“From the beginning, we believe, there was a rush to judgment by government officials and others in favor of . . . approval, despite decidedly mixed studies” regarding whether the drug really prevents HIV infection.

Gilead-sponsored studies show that, if taken daily, Truvada reduces the risk of infection by more than 90 percent. One Gilead study was stopped early, however, because women were not taking Truvada as prescribed — and hence were not protected against HIV. The drug can cause intestinal discomfort and diarrhea and, in rare cases, liver damage, which may explain why study volunteers stopped taking it.

FDA approval of Truvada for HIV prevention would mark a watershed moment in the fight against an epidemic that causes 50,000 new infections a year in the United States. According to the United Nations Program on HIV/AIDS, 2.7 million new infections occur annually worldwide.