UNITED NATIONS - The beleaguered African Union peacekeeping force in Darfur is on the verge of collapse, a development that is undercutting international efforts to protect civilians and deploy U.N. reinforcements to the troubled region in Sudan, according to African Union and U.N. officials.

The African Union's first major peacekeeping mission - once considered the last line of defense for Darfur's civilians - has been crippled by funding and equipment shortages, government harassment, and an upsurge in armed attacks by rebel forces that last month left seven African troops dead.

The setbacks have sapped morale among peacekeepers, many of whom have not been paid for months. It has also compelled the force - which numbered 7,000 troops at its peak - to scale back its patrols and has diminished its capacity to protect civilians, aid workers and its own peacekeepers.

In one example, Gambian troops last month failed to aid a Ghanaian peacekeeper who was gunned down in a carjacking within 300 yards of the mission's Darfur headquarters, U.N. officials said.

The crisis comes as the Sudanese government has renewed aerial bombardment in Darfur. And it has raised serious concerns among U.N. planners and outside experts about the viability of plans to deploy a joint U.N. and African Union peacekeeping mission of up to 20,000 troops. Some governments that have committed to send troops and equipment to Darfur are either balking or failing to make good on their pledges.

"The risk is great that everything will collapse," Alpha Oumar Konare, the African Union chairman, warned last month during Darfur talks in New York. "Today, we have soldiers who have been waiting three or four months to be paid."

The violence in Darfur erupted in February 2003, when the Sudanese Liberation Army and another rebel group took up arms against the Islamic government, citing discrimination against black tribes. Sudan responded by training and equipping an Arab militia, known as the Janjaweed, that killed hundreds of thousands of civilians suspected of backing the rebels and drove 2.5 million more from their homes.

The Bush administration has accused Khartoum of genocide and has argued that an expanded U.N. role in Darfur is key to ensuring the population's safety.

The AU presence - known as the African Mission in Sudan - was established in 2004 to monitor the violence and to prevent abuses against civilians and humanitarian-aid workers in Darfur. The force quickly endeared itself to Darfur's displaced civilians, escorting women to forage for firewood, reporting atrocities, and mediating between warring factions.

But it has been plagued for several months by chronic shortages of funds and supplies, forcing members to patrol in jeeps without radio communications and borrow soap and food from private charities and U.N. humanitarian agencies.

Last month, five Senegalese soldiers were gunned down by members of a rebel faction, according to Senegalese and African Union officials. Others have been beaten and robbed. One AU officer has been held hostage since December.

To improve security, Rwanda and Nigeria committed last year to send an additional 1,500 troops to Darfur to reinforce the mission.

Rwanda and Senegal have warned that they may withdraw if they do not receive financial support for the mission from Western donors.

"Things are not good, and the international community needs to act," Rwandan President Paul Kagame told Reuters last week.