U.S. voters are becoming increasingly concerned about North Korea's development of nuclear weapons and its long-range missile capabilities. In the latest Rasmussen Reports national telephone survey, 38% think North Korea is the biggest threat to U.S. national security, surpassing Iran by a more than two-to-one margin on voters' worry list.

In early May, only 23% of voters saw North Korea as the biggest threat, while 35% gave Iran that title.

Now 17% of likely voters say Iran is America’s biggest national security threat, while 12% view China that way. Another eight percent (8%) say Pakistan is the biggest threat. Only four percent (4%) each rank Iraq and Afghanistan, where U.S. troops are actually fighting, at the top of the list.

Just after President Obama was elected in November, only seven percent (7%) of voters thought North Korea would be the first nation to test him with an international crisis. In April, 57% of voters supported U.S. military action in order to eliminate North Korea's missile capabilities

As North Korean officials continue to threaten South Korea and its allies with a nuclear war, South Korean President Lee Myung-bak is expected to meet with Obama on Tuesday in Washington to seek a written promise of U.S. protection.

(Want a free daily e-mail update? If it's in the news, it's in our polls). Rasmussen Reports updates are also available on Twitter.

Pluralities of Democrats, Republicans and voters not affiliated with either party all now see North Korea as the biggest threat to national security.

When it comes to the fight against terrorism in the Middle East, 49% of all voters now say the United States and its allies are winning. That’s down from 52% two weeks ago. Twenty-two percent (22%) say the terrorists are winning the War on Terror, up four points from the last survey. Another 22% say neither side holds the advantage.

Forty-two percent (42%) of voters say the situation in Afghanistan will get worse over the next six months. Half as many (21%) say the situation will get better, and another 21% say it will stay about the same.

Just after the president announced his deployment of 17,000 additional troops in Afghanistan, 61% of voters agreed with his decision. Eighty-three percent (83%) say it is likely the president will have to send even more U.S. troops to Afghanistan in the next year or so. That's up nine points from March.

Voters are a little more optimistic about Iraq. The plurality (38%) says the situation is Iraq will get better in six months, while 25% say it will get worse. Nearly the same percent (24%) say nothing will change during that time. Those numbers are only slightly more optimistic than the last survey, when 36% said the Iraq situation would improve and 27% said things would get worse.

Forty-seven percent (47%) of voters say the United States is safer today than it was before the September 11, 2001 terrorist attacks, showing little change from the last survey. Thirty-five percent (35%) disagree, up slightly from two weeks ago.

The president earns good or excellent ratings from 47% of voters for his handling of national security issues. Twenty-nine percent (29%) say he is doing a poor job.

Please sign up for the Rasmussen Reports daily e-mail update (it’s free) or follow us on Twitter. Let us keep you up to date with the latest public opinion news.

See survey questions and toplines. Crosstabs are available to Premium Members only.