Colonel Gaddafi must be giving thanks to the climate-change gods for the weekend’s earthquake and tsunami in Japan, which has comprehensively diverted the world’s attention away from his military campaign to retake Libya from the opposition.

It’s impossible to get a clear fix on just how that campaign is going.

According to the latest BBC report, the “sound of rocket fire has been getting louder” in the opposition-held city of Ajdabiya, the gateway to eastern Libya. Pro-Gaddafi forces have apparently also retaken Zuwara and gained the upper hand in the battle for Brega, which “has changed hands several times over recent days”.

It is clear, however, that in purely military terms — planes, tanks and heavy artillery — Gaddafi has huge advantages over his opponents, and that the opposition is urgently calling for some form of international assistance — most commonly debated in terms of a no-fly zone to be imposed by Western air power. The Arab League has also supported such a move.

Western reluctance on this score is understandable. With the examples of Iraq and Afghanistan firmly in mind, no one wants to repeat the experience; US defence secretary Robert Gates made that clear in a speech last month. But Libya is a very different sort of case.

As my friend Guy Rundle keeps pointing out there’s a huge moral difference between, on the one hand, intervening to support people who are doing most of the fighting themselves and have specifically asked for help, and on the other hand imposing your “assistance” on people who either didn’t ask for it or weren’t going to do anything on their own.

Failure to understand this is widespread on left and right; a glaring example is conservative pundit Daniel Larison, who correctly diagnoses the shortcomings of the Iraq war but then blithely asserts that advocates of Libyan intervention “are calling for more or less exactly the same thing”.

And while it’s easy to talk about a “slippery slope” of gradually escalating intervention, there are no clear recent cases of that happening. Iraq was planned as a ground invasion from the start, while air power alone secured the Serbian withdrawal from Kosovo. Even in Afghanistan the Taliban was driven from power before there was any significant commitment of American ground forces.

Libya is also in a very different legal category. The Iraq invasion (as most people now admit) was a clear violation of the most basic precepts of international law. In Libya, however, there is already a war in progress: while there is a duty on other countries to avoid fuelling the fire, they are not obliged to stand by and watch as atrocities are committed and the popular will is overborne by armed force.

So far France has led the way, recognising the opposition as the legitimate government of Libya — a justifiable move given the opposition’s clear popular support, its control of territory and the allegiance of a large number of Libya’s diplomats.

International recognition opens the way to arms supplies and other logistical support to the opposition, but even on its own it would be a significant morale boost. As Carne Ross explained last week in The Nation, there are several things the West could be doing short of actual military intervention; some of these are probably already under way, but much more could be done without waiting for the cumbersome process of UN decision making.

Such measures would reassure the Libyan opposition that they are not alone; more importantly, they would put Gaddafi’s forces on notice that they are playing a losing hand and that the international community is determined not to allow them to prevail. The announcement of a no-fly zone, even if enforcement of it was only patchy, would carry the same message.

Barack Obama’s natural cautiousness has generally stood him in good stead, but this is one of those cases where holding back until a consensus has been fully formed means taking an unacceptable risk of disaster. Libya will not be Iraq or Vietnam, but if the West averts its eyes it could be Sarajevo or even Rwanda.