PANMUNJOM, North Korea -- As they gaze across the border at their American enemies, the North Koreans make jokes about the obesity of the U.S. soldiers.

But they also issue a grave warning. They say that the world's most heavily militarized region is becoming more dangerous than ever.

The confrontation line between North and South Korea is the last frontier of the Cold War, with more than 1.2 million troops -- including 37,000 Americans -- within striking range of each other. And now there is the nuclear factor.

"The United States is making excuses to invade us," a pistol-packing military officer at the border said. "They say we have nuclear weapons."

The peninsula already has the world's greatest concentration of troops and heavy armaments. The vast majority of the 1.8 million soldiers in the two opposing armies are within 60 miles of the border. North Korea now very likely possesses as many as six nuclear weapons, according to U.S. reports, and its nuclear program could produce dozens more warheads in the next few years. Last month it threatened to test a nuclear weapon, a step that would probably trigger a U.S. response.

The United States, meanwhile, heightened the tensions by announcing an $11 billion upgrade of its armed forces in South Korea, including the installation of a new state-of-the-art Patriot missile-defense system last week. It also spearheaded a multinational military exercise this month to practice intercepting North Korean ships at sea.

Former U.S. President Jimmy Carter warned that the Korean nuclear crisis is the biggest threat to peace in the world today. He said that some of the latest U.S. actions, including its missile-defense deployment and its military exercises, have given North Korea a legitimate reason to fear a pre-emptive invasion, similar to the U.S. attack on Iraq.

North Korea's expectations of war have been mounting ever since President Bush branded it part of the "axis of evil." Generations have been indoctrinated with an anti-American hatred, and now the hatred is being whipped up to new heights.

In cities across North Korea, propaganda signs portray the United States as a loathsome foe. A billboard in Pyongyang shows U.S. missiles and soldiers being crushed by a giant North Korean hand. A billboard in the port city of Wonsan shows a North Korean boxer knocking out a U.S. soldier.

In shops, history books are emblazoned with the phrase: "Wipe out the U.S. imperialist aggressors, the sworn enemy of the Korean people!" Every issue of the weekly Pyongyang Times contains articles denouncing the United States as a nation of sinister plotters and brutal war criminals. Newly published books accuse the United States of being "the empire of terrorism."

Even the thousands of children who attend the Pyongyang circus are indoctrinated with the same message. In the clown act at the circus, a drunken U.S. soldier -- a clown in a blond wig -- is the buffoon for a shrewd Korean clown who repeatedly kicks him from behind.

At a museum in the border zone, visitors are told the United States was the first to provoke the war in 1950, and the first to seek a cease-fire a year later. A photo of a grieving U.S. general is displayed there, too.

This ceaseless anti-American message helps North Korea justify its "army first" policy, which gives highest priority to its military in all matters. More than 30 percent of its GDP is devoted to the military -- the highest percentage in the world. In addition to its million active soldiers, its army includes about 3,500 battle tanks, more than 10,000 heavy artillery pieces, and about 5 million reservists.

Traveling across North Korea confirms that it is still the world's most heavily militarized country. The country appears to be in a constant state of alert. There are electrified fences at the border and along the beaches on the sea coasts, as if the Americans might come storming ashore at any moment.

The Pyongyang subway system is essentially a huge network of bomb shelters, with most stations at least 100 meters below the surface. Every village reportedly has a bomb shelter.