The United States is willing to alter the terms and conditions of its proposal to resolve the impasse over North Korea's nuclear programs, if the government in Pyongyang constructively outlines its concerns when talks resume at the end of this month, U.S. officials traveling with Secretary of State Condoleezza Rice said Sunday.

The U.S. proposal, offered in June 2004, had been denounced by North Korea as unbalanced because the government would have been required to disclose all of its nuclear programs, and have its claims verified, before the United States took any steps in return. The officials, briefing reporters on condition of anonymity, said they wanted to hear from North Korea whether new incentives needed to be added to a final deal and how the sequencing of reciprocal steps could be rearranged to suit North Korea's interests.

"It was a proposal, not a demand," one official said. "It was to get things started, which is why it is important to hear back."

China and South Korea, two key players in the six-nation talks, have repeatedly urged the Bush administration to show greater flexibility; the officials' remarks appeared aimed at addressing that concern. But the officials also suggested North Korea must be prepared to negotiate; otherwise, the administration could use the failure of the talks to seek support from regional allies for imposing punitive sanctions on North Korea.

Rice, speaking to reporters in Beijing after meetings Sunday with top Chinese officials, warned the North Korean government that it must demonstrate it is willing to bargain hard. "It is not the goal of the talks to have talks," she said. "It is the goal of the talks to have progress."

In an interview with Fox News before departing Beijing for Thailand, Rice said the reclusive government had "a bar to pass" after boycotting the process for more than a year. "We should not spend too much time celebrating the fact we are going back to the talks," she said.

U.S. officials caution that they are still not sure whether North Korea's willingness to return to the talks -- five months after the government swore it would never do so -- indicates a genuine desire to negotiate an end to its nuclear programs or is yet another stalling tactic that would allow it to build up its nuclear arsenal. Some U.S. officials are convinced North Korea will never give up its nuclear programs, no matter what concessions are made. Others believe it is necessary to test North Korean intentions.

U.S. hopes have been dashed before. Last year, after then-Secretary of State Colin L. Powell met with his North Korean counterpart at a regional forum to tout the administration's proposal for ending the impasse, a top U.S. official said that all that was necessary was to negotiate "how much money should be left on the bedside table." Instead, North Korea balked and refused to meet again for 13 months.

North Korea's decision to return to the negotiating table was sealed during a three-hour dinner in Beijing Saturday between a U.S. envoy and a top North Korean official. Much of the discussion centered on what Rice called the "modalities" of the talks -- setting a course that would allow for successive rounds of talks that build on their own momentum. The three previous sessions were held months apart, with North Korea returning to another round only after much cajoling -- and a huge infusion of cash and concessions from China.

U.S. officials traveling with Rice said that the increasingly desperate economic conditions in North Korea appeared to be a factor in its decision, though one said there was "no arm-twisting event." China recently refused a U.S. request to temporarily halt oil deliveries, but it has also tightened export controls, depriving North Korea of goods, one official said. At last month's South Korea-North Korea unity meeting, Seoul did not provide the expected huge aid infusion, another official said. "There was no enormous bonanza," he said, which was a signal.

At the unity meeting, the Seoul government did suggest it could provide a massive aid package to build up North Korea's electricity supply -- what South Korean media have dubbed a Marshall Plan -- but only if North Korea gave up its weapons. A top South Korean official also pointedly noted that the package would not include nuclear power.

The South Korean energy proposal showed North Korea there was "a path ahead if they want to take advantage of the six-party talks," Rice said in Beijing.