The top U.S. envoy to nuclear talks with North Korea conceded Wednesday that the communist nation's disarmament would be difficult to achieve this year, clouding the future of the process given the looming change in the White House.

"Completing everything by the end of the year will be a challenge and we need to see if it's going to be possible," U.S. Assistant Secretary of State Christopher Hill said after two days of meetings with North Korean nuclear envoy Kim Kye Gwan in Beijing.

The nuclear talks with North Korea that began in 2003 have been fraught with repeated setbacks and delays. The North has stopped making plutonium and begun disabling its nuclear facilities so they cannot be quickly restarted. But it still has a stockpile of radioactive material that experts believe is enough to make about a half-dozen bombs.

The North missed a deadline at the end of last year to give a full accounting of its nuclear programs. Washington had hoped they would be dismantled by this year, allowing President Bush to claim a rare diplomatic success before leaving office in January.

But at their latest talks in Beijing, the U.S. and the North were still trying to hash out a timeline for the declaration of nuclear programs to be dismantled, along with American concessions that include removing Pyongyang from terrorism and economic sanctions blacklists.

"We all have obligations and we all need to make sure as we go forward here that everyone has the sense that they are getting something positive out of the progress," Hill said.

Hill said meetings on technical issues would be required over the next couple of weeks before the North would submit the declaration. He declined to say exactly when that would happen.

"Things are moving ahead, but I'm not in a position really to talk about a timetable," Hill said.

The declaration also has been delayed over disagreements about what it should contain.

The U.S. had previously insisted that it include North Korea's alleged uranium enrichment program and nuclear cooperation with Syria. But Washington has apparently backed down from those demands, drawing strong conservative criticism at home.

North Korea has given the United States thousands of documents from its Yongbyon reactor, which were being reviewed to determine how much plutonium was produced there so that can be confirmed with its eventual declaration.

In Beijing, Hill also met with Chinese and Japanese envoys and will fly Thursday to Moscow to meet Russian officials and the South Korean nuclear envoy. All are involved in the six-nation talks on North Korea's nuclear programs.