AGHDAD, Iraq, April 22 - Some leading Kurdish political figures are trying to stall the formation of a new Iraqi government in an effort to force out Ibrahim al-Jaafari, the Shiite chosen two weeks ago as prime minister, Iraqi and Western officials said.

Such an effort could further delay forming a government at a sensitive time. The past week has seen a sharp increase in insurgent violence, including the downing Thursday of a commercial helicopter that left 11 people dead. One of the victims was apparently executed by the attackers.

American officials say the continuing failure to form a new government - almost three months after elections - could be contributing to the resurgent violence.

The political momentum generated by the elections has "worn off a bit," an American official here said Friday, and that "has given the insurgents new hope. The best thing to undermine the insurgency is to maintain momentum on the political process."

A spokesman for the Kurdish alliance denied Friday evening that there was any effort to unseat Dr. Jaafari. But Kurdish leaders have never been comfortable with religious figures like Dr. Jaafari, the leader of one of Iraq's best-known Shiite religious parties. Any successful campaign against him could derail the pact between the Shiite and Kurdish alliances that emerged two months ago, opening the possibility of a new alignment that would favor more secular figures like the departing prime minister, Ayad Allawi.

The American official said Friday that he expected that a new government would be formed within the next week with Dr. Jaafari as prime minister.

But several Iraqi political figures said they doubted that would happen. They cited strong opposition to Dr. Jaafari in the Kurdish alliance, which has agreed to form a coalition government with the Shiite majority. Under Iraq's transitional law, Mr. Jaafari will automatically lose his position if he does not name a cabinet by May 7, a month after his appointment.

"The Kurds are intent on delaying the government so that Jaafari will fall," said Sami al-Askari, a member of the Shiite alliance. A Western diplomat in Baghdad confirmed the effort to "filibuster" the negotiations.

Shiite officials say Kurds who oppose Dr. Jaafari offer several reasons, including a growing conviction that he does not favor the kind of federal arrangement that would allow for strong Kurdish autonomy.

If Dr. Jaafari is displaced, Iraq's new president, Jalal Talabani, a Kurd, and his deputies would then be forced to choose a new prime minister, the most powerful job in the government.

That would be a significant setback for the national assembly, which took more than two months just to agree on a new leadership. The delay sowed deep anger and disillusionment among ordinary Iraqis, who risked their lives to vote.

A further delay would stir more public rancor, and would further complicate efforts to meet the Aug. 15 deadline for drafting a new constitution.

Already, American officials say, the continuing absence of a new government may be strengthening the hands of insurgents, who launched more deadly attacks on Friday, including a car bombing outside a Shiite mosque in southern Baghdad that killed at least 9 Iraqis and wounded 26.

With the interim government led by Dr. Allawi in limbo, Iraq is suffering from something of a political vacuum. Local governments in several areas are showing signs of disorder, with some police officials acting independently of the federal government, the American official said.

Dr. Jaafari has always had some opponents among the Shiites.

But it is mostly Kurds who have led the new effort to oust him from the prime minister's seat, Shiite officials say. Late last month, Massoud Barzani, the leader of one of the two major Kurdish parties, made clear that he was deeply opposed to having Dr. Jaafari as prime minister, said a Shiite official.

"We cannot trust this man," Mr. Barzani said of Dr. Jaafari, according to the Shiite official.

The Kurdish opposition stems in part from a perception that Dr. Jaafari favors a strong centralized government and might not allow the Kurds the kind of regional autonomy they have enjoyed since 1991, Shiite leaders say.

It is true that last year, as a member of the American-appointed Iraqi governing council, Dr. Jaafari was one of several Shiite leaders who initially refused to sign Iraq's transitional constitution, saying he opposed a provision that would allow a two-thirds majority in any 3 of Iraq's 18 provinces to nullify the document in a referendum later this year. Dr. Jaafari, charged that the measure was undemocratic. Shiites represent 60 percent of Iraq's population.

He eventually signed, but said he might lead an effort to reverse the provision. That alarmed some groups here, including the Kurds.

Kurdish political figures, who tend to be secular, generally view Shiite religious groups such as Dr. Jaafari's Dawa Party with deep distrust, fearing that they will bring aspects of Islamic law into Iraq's legal code.

One important element has been the party of Dr. Allawi, which won 40 of the 275 seats in Iraq's national assembly in January.

The Shiite and Kurdish alliances agreed to try to include Dr. Allawi's party in the new government. But he has been insisting on four cabinet posts, including key positions such as the Defense or Oil ministries. He has also demanded a deputy prime ministerial position.

Shiite officials say Dr. Jaafari cannot offer that much to Dr. Allawi without facing a rebellion among the Shiites. But the Kurdish leadership insists that Dr. Allawi be accommodated, said Salam al-Maliki, a member of the Shiite alliance.

Shiite leaders believe the Kurdish alliance is using Dr. Allawi's party as a wedge to prevent the formation of a government, said Mr. Askari, the Shiite politician.