By Patrick Worsnip

UNITED NATIONS, Aug 31 (Reuters) - The stakes are high for U.N. Secretary-General Ban Ki-moon when he tours Sudan, Chad and Libya next week to try to smooth the way for a peacekeeping force he hopes will end the 4-year-old conflict in Darfur.

Ban has set ambitious goals for his six-day trip, saying he wants to lay the foundations of a lasting peace in the western Sudanese region, where an estimated 200,000 people have died and 2.5 million been driven from their homes.

The conflict began when mostly non-Arab rebels took up arms in Darfur, accusing Khartoum of neglecting the region, and the government mobilized mostly Arab militias to quell the revolt. Aid agencies say one of the world's worst crises has resulted.

Sudan agreed in July to the dispatch of a 26,000-strong joint U.N.-African Union force of troops and police to replace 7,000 existing AU peacekeepers who have been unable to cope. It is not expected to deploy before the new year.

But Western diplomats on the U.N. Security Council remain cautious, saying Sudan has made agreements before with the world body, only to cause problems later over the details of their implementation.

Ban, who arrives in Sudan on Monday, has acknowledged that Khartoum has the power to make the peace plan fail. It "cannot succeed without the cooperation of the government of Sudan," he told a news conference on Tuesday, adding that he would press President Omar Hassan al-Bashir for that support.

Despite a peace conference planned for October, a surge in violence in Darfur has claimed hundreds of lives in the past month, with rebels accusing the government of a daily bombing campaign. The armed forces have declined comment.

Khartoum also has ordered out European Union and Canadian envoys for what it said was interference in its affairs, as well as the country director of the U.S.-based CARE aid organization.

TOP PRIORITY

Ban's visit to Darfur will include a stop at a refugee camp. He also will travel to south Sudan, which has been semi-autonomous since a 2005 peace agreement ended 20 years of north-south fighting.

Problems have loomed in the south, too, with the northern army missing a July 9 deadline to move its troops out of vital southern oil areas.

Diplomats say Ban has made settling the Darfur conflict the top international priority of his eight months in office so far and the Africa trip commits his prestige to that task.

The diplomats say Sudan is now a critical test case for the United Nations itself. "If Darfur slips back into chaos and the north-south agreement falls apart, the U.N. as a whole will slip back," a senior Western envoy said this week.

The leaders of Britain and France revived the threat of sanctions in a joint newspaper editorial on Friday if Khartoum does not comply. But many Security Council members oppose sanctions as long as a peace process appears to be under way.

Ban also will go to Chad, which neighbors Darfur and hosts tens of thousands of refugees from there, to help put in place what he sees as the second prong of his strategy -- deployment of a peace force there to tackle the spillover from Sudan.

Because Chadian President Idriss Deby objected to U.N. forces, European Union troops will provide the military muscle for that mission for the first year under plans expected to be approved in Brussels in mid-September. But a question mark remains over what happens after that.

The U.N. chief winds up his tour with a 24-hour stopover in Libya, whose leader Muammar Gaddafi has hosted talks between Darfur's fractious rebel movements, which currently number about a dozen.

AlertNet news is provided by