WASHINGTON — North Korea may be a starving, friendless, authoritarian nation of 23 million people, but its apparently successful explosion of a small nuclear device in the mountains above the town of Kilju on Monday marks a defiant bid for survival and respect. For Washington and its allies, it marks a failure of nearly two decades of atomic diplomacy.

North Korea is more than just another nation joining the nuclear club. It has never developed a weapons system it did not ultimately sell on the world market, and it has periodically threatened to sell its nuclear technology. So the end of ambiguity about its nuclear capacity foreshadows a very different era, in which the concern may not be where a nation's warheads are aimed, but in whose hands its weapons and know-how end up.

As Democrats were quick to note on Monday, four weeks before a critical national election, President Bush and his aides never gave as much priority to countering a new era of proliferation as they did to overthrowing Saddam Hussein.

Bush and his aides contend that Iraq was the more urgent threat, in a volatile neighborhood. But the North's apparent nuclear test now raises the question of whether it is too late for the president to make good on his promise that he would never let the world's "worst dictators" obtain the world's most dangerous weapons.

"What it tells you is that we started at the wrong end of the 'axis of evil,"' former Sen. Sam Nunn, the Georgia Democrat who has spent his post-congressional career trying to halt a new age of proliferation, said in an interview. "We started with the least dangerous of the countries, Iraq, and we knew it at the time. And now we have to deal with that."

Bush's top national security aides declined on Monday to be interviewed about whether a different strategy over the past five years might have yielded different results. But Stephen J. Hadley, the national security adviser, has described the administration's approach to North Korea as the mirror image of its dealings with Iraq. "You'll recall that we were criticized daily for being too unilateral" in dealing with Saddam Hussein, Hadley said. "So here we are, working with our allies and friends, stressing diplomacy."

But at the same time, he said that the administration had made a conscious decision not to draw "red lines" in dealing with Kim Jong-Il's government because "the North Koreans just walk right up to them and then step over them," just to show they can. Other aides say that, lines or no lines, the North simply decided to race for a bomb — and finally made it.