UNITED NATIONS — The Security Council started preparing a new resolution yesterday that — once passed, and barring further political complications — would allow the deployment of troops to protect civilians in the Darfur region of Sudan to begin in six months. According to conservative estimates, 4,000 people are killed monthly in the Sudanese province.

British and other Western officials soon are expected to present a new draft resolution to the council’s 15 members, which will set the terms of deployment for a nearly 25,000-troop force, known as a “hybrid” because it would include contingencies from both African Union and the United Nations.

The Belgium’s ambassador to the United Nations, Johan Verbeke, who currently holds the rotating presidency of the Security Council, said he hoped the resolution proposal would be circulated by tomorrow or early next week. European and American diplomats say they want to guarantee that the rules set forth in the new resolution are clear enough to avoid any loopholes that would allow Sudan’s government to renege on its recent promises to let the hybrid force in.

“We should leave out any ambiguity,” Mr. Verbeke said, speaking to reporters yesterday after the council was briefed about the expected composition of the new force, specifically about the complex chain of command that would allow the United Nations to maintain overall control of the force while African Union commanders keep operational controls.

The issue is contentious because Khartoum at first declined to accept a U.N.-controlled force. Only after personal interventions by Secretary-General Ban and others, and a recent visit to Sudan from Security Council ambassadors, did the government finally say it would accept the force’s composition so long as the force keeps its “African nature.”

During the U.N. ambassadors’ visit to Khartoum, the foreign minister of Sudan, Lam Akol, told Security Council representatives “in no uncertain terms, that the government of Sudan accepted the hybrid operation without any conditionality,” one participant, South Africa’s ambassador to the United Nations, Dumisani Kumalo, said.

But once the council visit ended, Mr. Akol said in several public appearances that Sudan would condition its acceptance of the force on assurances that the new force would include no “khawagas” — a derogatory Arabic term for European colonialists.

In Sudan, there are currently 7,000 African Union troops that are expected to become part of the hybrid force. A separate vanguard of 2,200 soldiers and 700 police is expected to arrive soon to prepare the ground for the larger deployment. Tomorrow, the U.N. Department of Peacekeeping Operations will convene potential contributors from around the world, hoping that 15,000 more troops would be pledged.

“It is very difficult to give a precise timeline because there are many factors we do not control,” DPKO’s second in command, Hedi Anabi, said after being asked when the hybrid force would actually arrive in Darfur. “We hope we can start deployment within six months,” from the passage of the council resolution, he said.

U.N. officials estimate that about 200,000 have been killed since 2003. While several human-rights organizations estimate the toll to be much higher, the lower estimate would mean an average of 4,000 deaths each month.