SEOUL, South Korea - The CIA told members of Congress last week that North Korea's uranium-enrichment program, discovered this summer, would produce enough material for weapons in two to three years. The CIA also says North Korea has two weapons that were created before a previous program was halted by the United States in 1994.

But the CIA didn't mention how one of the world's poorest and most isolated nations assembled such complex technology.

According to officials interviewed in the past three weeks in Washington, Pakistan and Seoul, North Korea managed the feat through a relationship with Pakistan - a series of transactions that now appears much deeper and more dangerous than the United States and its Asian allies first suspected.

Pakistan's military ties to North Korea go back to the 1970s.

But they took a decisive turn in 1993, just as the United States was forcing North Korea to open its huge nuclear reactor facilities at Yongbyon. Yongbyon was clearly a factory for producing weapons-grade plutonium from spent nuclear fuel.

When North Korea refused to allow inspections led by Hans Blix, who is now in Iraq, President Bill Clinton went to the United Nations to press for penalties. The Pentagon drafted contingency plans for a strike against the plant.

In the midst of the standoff, Benazir Bhutto, then the prime minister of Pakistan, arrived in Pyongyang, the North Korean capital. She left with plans for North Korea's Nodong missile, according to former and current Pakistani officials.

Months after Bhutto's visit, the Clinton administration and North Korea reached a deal.

North Korea agreed to freeze all nuclear activity at Yongbyon, where international inspectors still live year-round. In return, the United States and its allies promised the nation a steady flow of fuel oil and the eventual delivery of two proliferation-resistant nuclear reactors to produce electric power.

But three years later, North Korean leader Kim Jong Il had grown disenchanted with the agreement and feared that the nuclear power plants would never be delivered.

By 1997 or 1998, American intelligence has concluded, he was searching for an alternative way to build a bomb, without detection. He found part of the answer in Pakistan, which had become a regular customer - along with Iran, Libya, Yemen, Syria and Egypt - for North Korean missile parts, American military officials said.