Early Sunday, allied warplanes, including U.S. air force fighters, destroyed a column of Libyan tanks and other vehicles set to attack the rebel stronghold of Benghazi.

Monday the rebels drove forty miles down the coast to Ajdabiya, where they were pushed back by government forces employing rocket and tank fire. According to the New York Times, allied warplanes flew overhead but didn’t attack.

Why provide air support in one situation and not the other?

It appears that the coalition’s rules of engagement allow the former because it is seen as consistent with U.N. Security Council Resolution 1973’s authorization of force to protect civilians. The latter counts as close air support, which is not authorized.

In essence, we are helping the rebels when they defend towns but not when they try to take them. It now seems unlikely that either side can win under those circumstances. So, rhetoric about ousting Gaddafi notwithstanding, our policy serves to stalemate the civil war, effectively severing Libya. That seems a recipe for a long stay.

This mismatch of means and ends results from the pretense that we are intervening to stop violence rather than taking a side in a civil war. The fact that coalition-building encouraged the pretense does not make it smart. The Secretary of State argues that our actions will pressure Qaddafi’s supporters in Tripoli to oust him. But it’s not clear why our rigorously defensive stance would embolden them. Having stayed loyal weeks ago, when the regime was shakier, they are unlikely to quit now.

I would have preferred for the United States to stay out of this civil war but for intelligence support and advice to the rebels. If we can disengage and leave the bombing to the Europeans, I hope we do so. But whoever is taking the lead should acknowledge that they are sponsoring rebels aiming to overthrow Qadaffi and adopt a policy that does more than defend them. The allies should give the rebels close air support and maybe strategic bombing. If that means abusing the words of the U.N. resolution, so be it. If it costs the support of the Arab League and whoever else supports air strikes based on the pretense that they are purely humanitarian, it’s probably a trade worth making.

I still naively hope for a Congress that at least would force public consideration of these issues through exercise of its constitutional powers.