(Adds British Muslim peace initiative and student arrests)

By Opheera McDoom

KHARTOUM, April 17 (Reuters) - Attacks by armed bandits on humanitarian convoys in Darfur are forcing the United Nations to sharply reduce monthly food rations to almost 3 million people in western Sudan, the World Food Programme said on Thursday.

The world's largest humanitarian operation struggles every day with bureaucracy, fighting and banditry to help those affected by five years of rape, violence and murder, which has killed an estimated 200,000 Darfuris.

The relief operation has been successful with some 12,000 aid workers bringing horrific mortality rates down to below emergency levels.

But the constant threat of attack by armed men has led some agencies to withdraw and others to work under security conditions they said would not normally be tolerated.

WFP has had 60 trucks attacked since the beginning of the year with 26 drivers still missing and one killed last month.

"The United Nations World Food Programme announced today that it will be forced to cut monthly rations in Darfur starting next month," the agency said in a statement.

Distribution of cereals, pulses and sugar will be cut by half, with the calorie count per person reduced by 40 percent.

"Attacks on the WFP food pipeline are an attack on the most vulnerable people in Darfur," said Josette Sheeran, WFP's executive director.

"With up to 3 million people depending on us for their survival in the upcoming rainy season, keeping WFP's supply line open is a matter of life and death."

WFP said government police were accompanying some convoys and they hoped to increase that number.

"We're appealing to the rebel factions and their commanders who operate in other parts of Darfur to ensure security on the roads and to respect the neutrality of all people involved in the humanitarian effort," said Kenro Oshidari, WFP head in Sudan.

Rebel groups which have factionalised beyond recognition are often blamed for the looting as their supply lines are cut off by infighting or clashes with the government.

A Reuters witness has seen WFP trucks being used by some rebels in Darfur.

Rebel factionalisation is also a major reason for frustrated peace efforts in Darfur. A British Muslim delegation, led by Lord Ahmed, arrived in Khartoum on Thursday hoping to kickstart that process.

Saying his efforts would complement those of U.N. Darfur envoy Jan Eliasson and African Union envoy Salim Ahmed Salim, Lord Ahmed said he would be talking to Muslims of all tribes in Darfur to try to convince them to come to the negotiating table.

Ahmed is respected by Khartoum, which puts the death toll in Darfur at 9,000 and blames the Western media for exaggerating the conflict.

On Monday Sudanese police arrested 95 Darfuri students demonstrating against violence in Darfur and discrimination against them in Khartoum's universities, a student leader said.

The Sudanese Organisation Against Torture said it feared those arrested were being tortured. "At least some of those detained have suffered serious physical abuse in custody," SOAT said in a statement seen by Reuters on Thursday.

The Interior Ministry was not immediately available to comment. (Editing by Mary Gabriel)