But Kosovo’s prime minister, Ramush Haradinaj, is adamantly opposed to any territorial concessions. He has described the idea as “a shortcut to tragedy.” And his stand has proved a potent weapon in his long rivalry with Mr. Thaci.

The proposals are profoundly unpopular both with Serbs — most of whom continue to consider Kosovo a part of Serbia, one that holds a foundational place in its national story — and with Kosovars, who regard what is under discussion as a partition of their young country along ethnic lines.

In Kosovo, Mr. Thaci’s popularity has plummeted. He is denounced in graffiti across the capital, Pristina, as linked to President Vladimir V. Putin of Russia.

“Kosovo is not Crimea,” read one phrase in English.

Mr. Haradinaj has capitalized on resentment of what is sometimes seen as the president’s warm relationship with Serbia by moving in a direction that many say strengthens Kosovo’s statehood. In December, the Parliament overwhelmingly approved legislation to form an army, prompting criticism from NATO, which has been keeping a tense peace in the area.