“The entire region has a stake in Afghanistan’s future and much to lose if the country again becomes a source of terrorism and instability,” Mrs. Clinton told the delegates here, who included dozens of foreign ministers. “And that is why we could, of course, have benefited from Pakistan’s contribution to this conference.”

Another neighbor did attend: Iran. Its foreign minister, Ali Akbar Salehi, sat behind Mrs. Clinton as she spoke, though neither she nor other officials had any formal contact with the Iranians here. Mr. Karzai later teased Mrs. Clinton, saying the Iranians were “your friends” and that their speech had been kind.

(In fact, Mr. Salehi denounced the international military operation, though in perhaps milder terms than before. “Certain Western countries seek to extend their military presence in Afghanistan beyond 2014 by maintaining their military bases there,” he said, in remarks carried by Iran’s official Islamic Republic News Agency. “We deem such an approach to be contradictory to efforts to sustain stability and security in Afghanistan.”)

Ryan C. Crocker, the American ambassador to Afghanistan, accompanied Mrs. Clinton in her meeting with Mr. Karzai. He referred to Mr. Salehi’s remarks, saying to Mr. Karzai, “Mr. President, you call that kind?”

The conference, though far from Afghanistan, was, officially, led by Mr. Karzai’s government. It was held in the former Parliament building of West Germany. Across the Rhine protesters erected shiny letters spelling “End the War in Afghanistan.”

Mrs. Clinton, echoing several other ministers, reiterated the Obama administration’s view that there was no purely military solution to the conflict. Still, new efforts to encourage reconciliation with the Taliban — which also rely on Pakistani cooperation — appear moribund, especially since the assassination in September of Burhanuddin Rabbani, a senior Afghan official leading the reconciliation process, by a suicide bomber posing as a Taliban peace emissary. Even though President Obama and other NATO leaders have created a timetable for withdrawal by 2014, many officials worry about security and the stability of Mr. Karzai’s government once foreign troops leave. It could also have a devastating effect on Afghanistan’s struggling economy, which has come to depend on NATO spending.

Mr. Karzai’s government presented a paper at the conference, warning that the withdrawal could halve the country’s gross domestic product.