WASHINGTON - On three key flash points -- North Korea, Iran and Sudan -- the Bush administration confronts the possibility that its current diplomatic approaches have reached the end of their effectiveness, forcing it to consider potentially riskier "Plan B" alternatives, administration officials and outside experts said.

Six-nation talks on ending North Korea's nuclear programs ended in failure yesterday, suggesting the format could be scrapped after more than three years of inconclusive results. Today, after months of negotiations, the U.N. Security Council may finally approve a relatively weak resolution sanctioning Iran for its pursuit of nuclear power, freeing the administration to try a more unilateral approach to punishing Tehran.

And Sudan faces a U.S.-imposed deadline of Dec. 31 to comply with demands that it allow more peacekeeping forces in the troubled region of Darfur -- or else U.S. officials might move toward such options as imposing a no-fly zone over Darfur.

A senior administration official acknowledged yesterday that diplomatic approaches taken by Secretary of State Condoleezza Rice on these three issues may have hit real roadblocks. "It doesn't mean that you push aside what you have been doing," he said, but that the administration at the same time will look for other ways to tackle the problems.

No clear Plan B for Sudan
The options on Sudan -- where as many as 450,000 people have died and more than 2 million people have lost their homes in the Darfur region -- are also difficult if Sudan refuses to accept expanded peacekeeping forces. U.S. officials say one form of pressure will be pending indictments of Khartoum's leaders by the International Criminal Court. Another option is imposing a no-fly zone over Darfur, over the objections of Khartoum -- though that would require careful planning and probably the involvement of U.S. forces. China is a major investor in Sudan's petroleum industry and would be expected to block tough action at the Security Council.

Ivo H. Daalder, a senior fellow at the Brookings Institution, said the administration is confronting the limits of "traditional U.N.-reliant diplomacy," though he felt the administration had not invested enough time in devising true Plan B approaches for any of these issues. "Including Iraq, they have four real crises," he said. "But they have less leverage and less capability and less credibility to deal with any in a diplomatic way."