North Korea could conduct a nuclear test soon with either plutonium-based devices or highly enriched uranium, or with both, "a destabilizing event" that would prevent the United States from returning to negotiations but would not threaten the country, a former U.S. secretary of defense said Wednesday.

Pyongyang has vowed to conduct its third nuclear test in retaliation for the U.N. Security Council's resolution condemning its Dec. 12 long-range rocket launch, and there have been a series of signs indicating its imminent detonation.

Making good on the nuclear threat, the North issued a string of warnings that it will "target the U.S."

"I think they are technically ready or will be ready in a few weeks (for the nuclear test)," William Perry said in an interview with Yonhap News Agency. "It all depends on its political decision.

They have to decide their political cost of the test."

Perry, who served as Washington's point man on Pyongyang during the Clinton era, also noted that the North can make "a couple of bombs per year with its highly enriched uranium," adding it would either conduct "the first test with bombs made of high enriched uranium" or "the plutonium design they already have to make missiles," or they could do the both.

The former defense secretary, however, dismissed the notion that the North's long-range rockets or nuclear weapons will be a serious threat to the U.S.

"Suppose North Korea has 10 intercontinental ballistic missiles (ICBM), but how can they threaten the U.S. that has more than a thousand ICBMs? I don't think the North Korean government is suicidal," he said.

He also said any military options for the U.S. against Pyongyang are not practical, citing different circumstances now from some two decades ago. In 1994, Washington prepared for an attack on the North when the communist country was beginning to produce plutonium at its Yongbyon nuclear complex, and Perry himself was involved in the plan.

"In those days, all the North Korean nuclear facilities were in one place so that we can attack them with one strike. But now, facilities are spreading all over the country, and bombs could be moved around from place to place. So it's not possible today to eliminate all the nuclear capability," he said.

Just as the U.S. did back then, the military option is "always the last possible alternative," he said, advocating the launch of "an official dialogue."

"We need an official dialogue between senior officials of the U.S. and North Korea. Any unofficial dialogues can only be the stepping stone to the official one," he said.

"If North Korea goes ahead with the third nuclear test, that's going to be a very destabilizing event, and it's going to make it very difficult for the U.S. ever to get back into the negotiation position. It is going to make it almost impossible to start the Perry Process again," he said.

The former defense secretary is known for his 1999 proposal for a three-stage resolution to the North Korea's weapons of mass destruction, with the focus on the so-called Perry Process, which included freezing North Korea's missile activities and paving the way for normalizing relations between Pyongyang and Washington.

Guarding against the attitude of dealing with Pyongyang with "wishful thinking," he also stressed the countries involved should "put together a proposal to the North which offers incentives as well as threats."

Along with "the tripartite process with the U.S., South Korea and Japan coming together as one unit," he also called on the allies to understand the bigger role China now plays compared to 13 years ago.

"In my judgment, North Korea is building nuclear weapons with a new uranium process. It could be done on their own, but components of the centrifuges either are coming from Chinese companies or European companies shipped to China," he said. "So China plays a pivotal role to stop the North from the continued buildup of their nuclear arsenal."

Mentioning the 60th anniversary between South Korea and the U.S., Perry said the bilateral relations have "never been stronger," calling the bond "very positive" in the face of the crisis today.

He arrived in South Korea on Monday to meet with South Korean President Lee Myung-bak and President-elect Park Geun-hye, and to deliver a keynote speech the following day during the international conference on how to tackle pending security issues in Northeast Asia. 

The "Yonhap-Stanford APARC International Symposium," under the theme of "Northeast Asia under New Leadership," was co-hosted by Yonhap and the Asia-Pacific Research Center (APARC) of Stanford University, bringing together a number of former and current government officials from the allies. (Yonhap News)