But they warned vaccine supplies remain inadequate.
"Some things we will do include isolating people who are sick and perhaps quarantining their counterparts," Julie Gerberding, director of the national Centers for Disease Control and Prevention, told Bob Schieffer on CBS' "Face the Nation."
But she added: "Quarantine is a word that has a lot of bad meanings. ...I don't think any of us are thinking of draconian measures to completely quarantine a country or quarantine a community."
Read the transcript of the "Face The Nation" interview with Gerberding: View PDF Document
Asked Schieffer: "Is it an urgent threat … Is it just a matter of time before it gets to the United States?
Replied Gerberding: You know, I wish we knew the answer to that. We are very concerned about the H5N1 influenza that's in Asia and eastern Europe right now. We have no idea if it will become transmissible from one person to another efficiently, but we've got to take the steps now to get prepared for that.
"We've probably never been closer to a pandemic than the year in 1917. And so when we see the ominous signs of this very bad virus continuing to propagate there, we do need to take it seriously and solve some of the problems that would be in our way from effective response in the United States."
A strain of a bird flu that has killed more than 70 people in Asia since it first appeared two years ago has sparked concerns of a super-flu that could kill millions worldwide. Almost all the victims were in close contact with birds.
While stressing that chances remain slight, health experts have said it could lead to a global pandemic if the bird flu mutates to start spreading easily among people.
Health and Human Services Secretary Mike Leavitt, appearing on CNN's "Late Edition," said U.S. officials expect some strain of the virus will ultimately reach the United States, but could not predict when.
President Bush last week signed a bill that gives $3.8 billion to prepare for a possible outbreak of bird flu and liability protections for flu drug manufacturers. Leavitt praised that as good step that will fund one year of flu-preparedness efforts.
"We have to be prepared it will find the United States soon," said Leavitt, noting that manufacturing capacity for a vaccine remains limited. "The problem is getting vaccines in the arms of people. That's why state and local preparedness is so important."