WASHINGTON — President Obama said yesterday the U.S. is taking "all necessary precautions" to be prepared if the swine flu develops into "something worse" and has discussed with Mexico's president how to keep the flu strain from spreading.

This new strain of swine flu, or H1N1 flu as the government prefers to call it, has caused only one confirmed death in the United States. But because medical authorities fear the situation could get much worse, Obama said, he has thrown substantial federal resources against it.

"This is a new strain of the flu virus, and because we haven't developed an immunity to it, it has more potential to cause us harm," Obama said in his weekly radio and Internet address. "...This creates the potential for a pandemic, which is why we are acting quickly and aggressively."

The virus, which has claimed far more victims in Mexico than elsewhere, has not proven as potent in the U.S. "We cannot know for certain why that is, which is why we are taking all necessary precautions in the event that the virus does turn into something worse," he said.

He noted that this flu "can be defeated by a course of antiviral treatment that we already have on hand." One-fourth of the nation's 50 million courses of the treatment have been distributed to states, he said. Obama has asked Congress for $1.5 billion to buy more medicine and equipment if needed.

"It is my greatest hope and prayer that all of these precautions and preparations prove unnecessary," he said.