Among the first waves of rebels to storm Tripoli this week was a small team whose members carried smartphones along with their weapons. Under a well-rehearsed plan, they blasted Arabic text messages that would appear on tens of thousands of cellphones throughout the city.

“Don’t destroy public buildings,” one read. “These are for the future of Libya.”

The dissemination of the messages, intended to discourage looting and arson in liberated parts of the city, was among the lead items on a long to-do list that the rebels are just beginning to put into place. Developed and refined during multiple meetings in Washington, Benghazi and Doha, the list represents an attempt to anticipate every possible hiccup and challenge that could undermine Libya’s transitional government in its first weeks — from reprisal killings to power outages to sewage backups.

Anxious to avoid the anarchy that followed the fall of Baghdad in 2003, rebel leaders and their Western backers began planning five months ago for the aftermath of Moammar Gaddafi’s defeat, long before it was clear how, or whether, the Libyan autocrat would fall.

The rebels’ post-victory planning now faces the ultimate test as the Transitional National Council seeks to assert its authority amid the chaos of a capital that is still claimed by Gaddafi and contested by remnants of his once-vaunted security forces. U.S. officials say the results so far are encouraging; Tripoli’s civilian population has remained relatively subdued, and acts of wanton destruction have been few. But they acknowledge that much depends on circumstances that are difficult to control or predict.

“We’re at a pivotal transition point now,” Jeffrey Feltman, the State Department’s chief diplomat for the Middle East, said Wednesday as he shuttled between meetings on Libya in the Qatari capital of Doha. “There are a lot of challenges ahead, and security is only the first of them.”

A European diplomat involved in Libya policy discussions was struck by the amount of detailed discussion of “what needs to happen and who needs to do it.”

“Quite a lot of planning has been done already,” said the official, who spoke on the condition of anonymity to describe diplomatic discussions. “Now everyone is looking at activating all the planning.”

The planning for post-Gaddafi Libya, described in interviews with U.S. and European officials, began as early as mid-March, before U.N. approval of the NATO-led military intervention. Diplomats and security officials began to map out possible outcomes for what was then a one-sided conflict between powerful, well-trained Libyan troops and disorganized bands of anti-government protesters.

At that time, the likely scenarios ranged from an outright Gaddafi victory to a permanently divided Libya, with rebels maintaining control over a few eastern provinces, U.S. officials said. Only weeks later, after NATO fighter planes gave the rebels space to regroup, did the planners begin to think seriously about a future Libya in which the rebels were in charge.

U.S. and British officials independently began outlining separate visions for how the rebel alliance might assert control over a country with tribal and geographical divisions. In late April, as Western emissaries traveled to Benghazi for meetings with the fledgling TNC, it became clear that the opposition movement was already working through the same issues.

“The focus was on inclusiveness, the security dimension and restoring civil order,” said a senior Obama administration who was present at several of the sessions. Secondary but equally vital was the ability to provide basic services and restart the economy. “Each of these dimensions brought its own risks and challenges,” the official said.

By early summer, diplomats were traveling regularly to Benghazi and Doha with proposals and counterproposals for dealing with dozens of specific tasks. How, for example, would the rebels manage to restore electricity in Tripoli if major power plants were disabled? How would food supplies be stored and distributed? How would bureaucrats in Tripoli receive paychecks and fuel to heat buildings and run vehicles?

The idea of sending text messages came up early in discussions of how to pacify Tripoli in the hours after liberation. Some residents of the capital might be nervous about the rebels’ intent, and others could be tempted to attack police stations and other symbols of Gaddafi’s oppression, the planners knew.

“The messaging was the first task,” a second administration official said. “Basically, the rebels needed to say, ‘We’re here’ and ‘We’re all Libyans,’ reassuring a population that has grown up under Gaddafi.”

Security was viewed as equally vital, so some rebel units were assigned to patrol newly liberated areas to guard against violence and looting. The patrols were activated in Tripoli on Sunday, though their jobs have been complicated by the sporadic fighting and the phantom presence of Gaddafi.

“Finding and dealing with Gaddafi is important,” the European diplomat said. “Once that happens, I think Libyans can move on. While he remains at large, he remains a security threat and a rallying point for supporters and the old regime.”

Some tasks, such as food distribution, are logistically demanding, requiring resources and support from international agencies including the United Nations. But dealing with the world body brings its own complications, many of them legal.

While U.N. officials are prepared to establish a mission in Tripoli, they need a formal request from the new government. For that to happen, the TNC needs to declare itself the new government in Tripoli.

Both the European Council and NATO’s North American Council, the alliance’s political body, have been reviewing the rebels’ progress with a view to tweaking the transition plan as needed. Mid-level officials from the international contact group on Libya plan to meet Thursday in Istanbul to coordinate their efforts, with a ministerial meeting tentatively planned for next week in France.

While acknowledging that much could still go wrong, a NATO official said the alliance has been encouraged that there had been “relatively” little violence and reprisals in rebel-held areas around the country.

“Clearly, this phase we’re going into now is pretty critical,” the NATO official said. “But there’s a lot of international support there, a lot of international cohesion.”