Beijing - A senior Pentagon adviser has given details of a war strategy for invading North Korea and toppling its regime within 30 to 60 days, adding muscle to a lobbying campaign by U.S. hawks urging a pre-emptive military strike against Pyongyang's nuclear facilities.

Less than four months after the end of the Iraq war, the war drums in Washington have begun pounding again. A growing number of influential U.S. leaders are talking openly of military action against North Korea to destroy its nuclear-weapons program, and even those who prefer negotiations are warning of the mounting danger of war.

Some analysts predict that North Korea could test a nuclear warhead by the end of this year - an event that could cross the "red line" that would provoke a U.S. attack.

The tensions were heightened by a recent exchange of gunfire across the border between North Korean and South Korean soldiers. Talks between U.S. and North Korean officials are expected to be held in Beijing soon, but nobody is predicting an imminent diplomatic agreement, especially after North Korea denounced a U.S. negotiator as a "bloodsucker" and "human scum."

Military conflict in the Korean peninsula could trigger a catastrophe, not only because of the suspected presence of nuclear bombs in North Korea, but also because of the 11,000 North Korean artillery weapons along the border that could inflict death and destruction on millions of people in the South Korean capital, Seoul, which is within artillery range of the North's guns.

Former CIA director James Woolsey, a Pentagon adviser and close ally of Defence Secretary Donald Rumsfeld, gave the most explicit glimpse into the thinking of U.S. military planners this week when he revealed the details of a possible plan of attack against North Korea.

The plan would include 4,000 daily air strikes against North Korean targets, the deployment of cruise missiles and stealth aircraft to destroy the Yongbyon nuclear plant and other nuclear facilities, the stationing of U.S. Marine forces off the coasts of North Korea to threaten a land attack on Pyongyang, the deployment of two additional U.S. Army divisions to bolster South Korean troops in a land offensive against North Korea, and the call-up of National Guard and Reserve units to replace U.S. combat forces that are currently bogged down in Iraq and Afghanistan.

"Massive air power is the key to being able both to destroy Yongbyon and to protect South Korea from attack by missile or artillery," Mr. Woolsey wrote this week in the Wall Street Journal in an article co-written by retired U.S. Air Force Lieutenant-General Thomas McInerney.

"We believe the use of air power in such a war would be swifter and more devastating than it was in Iraq," the article said. "We judge that the U.S. and South Korea could defeat North Korea decisively in 30 to 60 days with such a strategy."

Mr. Woolsey and Lt.-Gen. McInerney said the U.S. should already be preparing "to assess realistically what it would take to conduct a successful military operation to change the North Korean regime."

They acknowledged the risk that U.S. military strikes could trigger an explosion of radiation from North Korean nuclear plants, along with massive artillery attacks against Seoul by the North Korean heavy guns that are hidden in hardened underground bunkers on the border.

But U.S. cruise missiles and stealth aircraft could launch precision bombing attacks that would "minimize radiation leakage" at Yongbyon, while also sealing shut the underground bunkers where the artillery pieces are hidden, they said.

They warned that a war could soon become necessary to prevent North Korea from selling weapons-grade plutonium to "rogue states" and terrorist organizations. "The world has weeks to months, at most, to deal with this issue, not months to years," Mr. Woolsey and Lt.-Gen. McInerney wrote.

Similar warnings were issued recently by William Perry, the former U.S. defence secretary, who said North Korea and the United States were drifting toward war - perhaps as early as this year.

Mr. Perry said the administration of U.S. President George W. Bush is "losing control" of the North Korean nuclear crisis, making it possible for Pyongyang to begin selling nuclear weapons to terrorists soon. "The nuclear program now under way in North Korea poses an imminent danger of nuclear weapons being detonated in American cities," he told The Washington Post.

He said North Korea seems to have begun reprocessing some of the 8,000 spent fuel rods from a closed nuclear plant. This could allow Pyongyang to build up to six nuclear bombs in the next six months. "I have thought for some months that if the North Koreans moved toward processing," he said, "then we are on a path toward war."