The only use of an atomic bomb - by the United States against Japan at the end of World War II - provokes sharply different reactions, depending on the age of those asked. Young adults tend to disapprove, while older Americans tend to approve, an AP-Ipsos poll found.
Albert Kauzmann, a 57-year-old resident of Norcross, Ga., said using the bomb in 1945 "was the best way they had of ending" World War II.
Six in 10 people age 65 and older approve of the use of the atomic bomb at the end of World War II; the same percentage of respondents 18 to 29 disapprove.
Even though the Soviet Union is gone, the nuclear fears that fueled the Cold War have not gone away. A majority of people believe it is likely that terrorists or a country will use the weapons within five years.
North Korea claims it has nuclear weapons now and is making more. Iran is widely believed to be within five years of developing such weapons. Security for the nuclear material scattered across the countries of the old Soviet Union remains a major concern.
Lurking in the background is the threat that worries U.S. officials the most: terrorists' desire to acquire nuclear weapons.
All that helps explain why 52 percent of Americans think a nuclear attack by one country against another is somewhat or very likely by 2010. Also, 53 percent think a nuclear attack by terrorists is at least somewhat likely.
The Bush administration repeatedly warns about nuclear weapons and is using diplomacy - and force - to try to limit the threat.
Two-thirds of respondents say no nation should have nuclear weapons, including the United States. Most of the others surveyed say no more countries should get the weapons.
"I worry about Pakistan and India," said Barbara Smith, who lives in a Philadelphia suburb. "I don't know what's going to happen with Iran, don't know what's going to happen with North Korea."
Smith said she wants to see the spread of nuclear weapons stopped. "It's too dangerous, too many things can go wrong," she said.
About one-third of those in an ABC News-Washington Post poll in the mid-1980s - when the Cold War was hot - thought there would be a nuclear war in the next few years between the two superpowers.
The AP-Ipsos poll found 44 percent of those surveyed said they frequently or occasionally worry about a terrorist attack using nuclear weapons, while 55 percent said they rarely or never do.
Susan Winter of McLean, Va., says her awareness of the nuclear threat does not cause her to fret constantly. "I'm concerned, but I don't worry about it," Winter said. "I'm not a nail biter. I don't lose sleep over it."
People were divided about the use of the atomic bomb in 1945, though they were asked about Hiroshima and Nagasaki after a series of questions on the nuclear threat.
Overall, 47 percent of those surveyed approved of dropping the bombs on Japan while 46 percent disapproved, according to the poll of 1,000 conducted by Ipsos-Public Affairs from March 21-23 with a margin of sampling error of plus or minus 3 percentage points.
The United States, Britain, Russia, France and China have nuclear weapons, and Pakistan and India have also conducted nuclear tests. Many believe Israel has nuclear weapons, but that country has never acknowledged it. North Korea claimed in February that it had nuclear weapons.
The threat from nuclear terrorism is greatest, analysts say, because terrorists with nuclear weapons would feel little or no hesitance about using them. That's why those who monitor nuclear proliferation are so concerned about securing weapons stockpiles and dismantling weapons as quickly as possible.
"We're in the race of our lives," said Joe Cirincione of the Carnegie Endowment for International Peace, "and we're not running fast enough."