Iraq's Kurdish leaders yesterday told a top U.S. envoy in Iraq that they want one of the two top positions in the new interim government -- president or prime minister -- or the Kurds will not participate in the body that is scheduled to take over when the United States hands over limited authority on June 30, according to Kurdish and U.S. sources.

The Kurds were slated to take a lower position, as one of two vice presidents, in a formula designed by U.N. special envoy Lakhdar Brahimi that the Bush administration hoped to unveil next week. But Jalal Talabani, a veteran Kurdish leader and one of 25 members of the U.S.-appointed Iraqi Governing Council, yesterday informed Robert D. Blackwill, the U.S. presidential envoy to Iraq, that the Kurds would not take the job, Kurdish and U.S. sources said.

The move is a setback that complicates U.S. hopes of winning agreement from Iraq's disparate ethnic and religious factions on the makeup of the interim government. Unless the Kurds back down or U.S. and U.N. envoys negotiate a compromise soon, the process of forming a government could drag on longer than expected -- and potentially deepen rivalries, experts on Iraq warn.

The Bush administration hopes that the Kurds are posturing and can eventually be brought around, rather than be blamed for sabotaging the third attempt to form a government.

"This is jockeying for position and status. It strikes me as politics. It's good to see and messy to watch," said a senior State Department official involved in Iraq policy. "It's how committee assignments get made in our Congress. It's part of working the process and the kind of thing you work through. Talks [on a new government] are proceeding apace."

But Talabani and Massoud Barzani, who lead the two main Kurdish parties, have together insisted that the Kurds have one of the top two positions to create balance with Iraq's majority Arab population.

"The two Kurdish leaders are united. We believe the Kurds can be a bridge between the Sunnis and the Shiites," said a senior Kurdish official who requested anonymity because of the sensitivity of the issue. The majority of Iraq's 25 million people are Shiite Muslim. Most Kurds are Sunnis, bolstering the Sunni minority that has felt marginalized since the ouster of Saddam Hussein.

"They don't want to be a token," said Lehigh University professor Henri Barkey. "There's no question that Barzani and Talabani are bargaining."

With the June 30 deadline looming and the Bush administration struggling to establish control, the Kurds believe they have valuable leverage -- and will use it, said Iraq scholar Phebe Marr. Their strongest tool right now is the power of delay.

"They're going to bargain as hard as they can. They think they've got us over a barrel because we're fighting on so many other fronts: the Sunni front, the Shiia front," said Marr, author of "The Modern History of Iraq."

The Kurds, long buffeted by more powerful neighbors, enjoyed 13 years of increasing autonomy and prosperity in a protected security zone since the Persian Gulf War. With Hussein's government gone and the Kurdish northern sectors being folded back into a united Iraq, Kurds are worried about losing power and influence.

Some analysts believe Kurdish politicians, who have formally forsworn long-standing demands for independence, will still seek as much autonomy as possible in negotiations over the interim government.

The Kurds are "willing to look at options as long as they have some autonomy and some real and symbolic identity," said Mark Schneider, senior vice president of the International Crisis Group.

"When you step back," Schneider continued, "is the balance going to be one in which the Kurdish representations at the national level reflect their view of their stake in the future of Iraq? Obviously, the negotiations will go to the last minute."

In his talk with Blackwill, Talabani argued that Kurds who have long been loyal to the Americans deserve respect and a better deal, particularly compared with the Sunni minority that ruled Iraq under Hussein. As Barkey put it: "The Kurds clearly have been the United States' best friend in Iraq."