In March of 1974, when I was a young Army captain, I was sitting in a conference on civil-military relations at Brown University. Rep. Les Aspin (D-Wis.) was onstage expounding on the lessons from Vietnam about military interventions. He then stopped and looked right at me and the four West Point cadets at my side. “You, the young officer and cadets sitting there — never in your lifetimes will you see us intervene abroad,” I recall him saying. “We’ve learned that lesson.”

For all his brilliance, Aspin couldn’t have been more wrong.

We have launched many military interventions since then. And today, as Moammar Gaddafi looks vulnerable and Libya descends into violence, familiar voices are shouting, once again: “Quick, intervene, do something!” It could be a low-cost win for democracy in the region. But before we aid the Libyan rebels or establish a no-fly zone, let’s review what we’ve learned about intervening since we pulled out of Vietnam.

The past 37 years have been replete with U.S. interventions. Some have succeeded, such as our actions in Grenada (1983), Panama (1989), the Persian Gulf War (1991) and the Balkans (1995-2000). Some were awful blunders, such as the attempted hostage rescue in Iran (1980), landing the Marines in Lebanon (1982) or the Somalia intervention (1992-94).

Some worked in the short run, but not the longer term — such as the occupation of Haiti in 1994. Others still hang in the balance, such as the wars in Afghanistan and Iraq, consuming hundreds of billions of dollars and wrecking thousands of American lives. Along the way, we’ve bombed a few tyrants such as Saddam Hussein and Gaddafi himself, operated through proxies in Central America, and stood ready with fly-overs, deployments, mobility exercises and sail-bys across the globe.

I’ve thought about military interventions for a long time — from before my service in Vietnam to writing a master’s thesis at Fort Leavenworth to leading NATO forces in the Kosovo war. In considering Libya, I find myself returning to the guidelines for intervention laid out by Defense Secretary Caspar Weinberger in 1984. The world has changed a great deal since then, so I’ve adapted and updated his vision to develop my own rules for when the United States should deploy its blood and treasure in operations far fromhome.

Understand the national interests at stake, and decide if the result is worth the cost.

We went into Lebanon with a reinforced battalion of Marines in 1982 because we believed that it was in our national interest to stabilize the situation after the Israelis had been forced out of Beirut. But after the terrorist bombing of their barracks killed 241 U.S. service members the next year, we pulled out. After the tragedy, any benefits seemed to pale in light of the cost and continuing risks.

In 1999, when we launched the NATO air campaign against Serbian ethnic cleansing in Kosovo, President Bill Clinton had to state publicly that he didn’t intend to use ground troops. He did so in an effort to limit the costs of an initiative that the public and Congress did not consider to be in our nation’s vital interest. The administration and I, as the NATO commander in Europe, were in a difficult position, and Serbian dictator Slobodan Milosevic knew it. But what Milosevic didn’t understand was that once we began the strikes — with NATO troops deployed in neighboring countries and the Dayton Peace Agreement to enforce in Bosnia — NATO couldn’t afford to lose. And the United States had a vital interest in NATO’s success, even if we had a less-than-vital interest in Kosovo.

In 2001, when the United States went into Afghanistan, it was clear that we had to strike back after the attacks of Sept. 11. And we’re still there, despite all the ambiguities and difficulties, because we have a vital interest in combating al-Qaeda and similar terrorist groups there and across the border in Pakistan.

How do we apply this test to Libya? Protecting access to oil supplies has become a vital interest, but Libya doesn’t sell much oil to the United States, and what has been cut off is apparently being replaced by Saudi production. Other national interests are more complex. Of course, we want to support democratic movements in the region, but we have two such operations already underway — in Iraq and Afghanistan. Then there are the humanitarian concerns. It is hard to stand by as innocent people are caught up in violence, but that’s what we did when civil wars in Africa killed several million and when fighting in Darfur killed hundreds of thousands. So far, the violence in Libya is not significant in comparison. Maybe we could earn a cheap “victory,” but, on whatever basis we intervene, it would become the United States vs. Gaddafi, and we would be committed to fight to his finish. That could entail a substantial ground operation, some casualties and an extended post-conflict peacekeeping presence.

Know your purpose and how the proposed military action will achieve it.

In 1989, when the United States wanted regime change in Panama, a powerful U.S. force took over the country, captured dictator Manuel Noriega and enabled the democratic opposition to form a new government. Panama today is a thriving democracy.

On the other hand, in Somalia in 1992-94, we started out on a humanitarian mission, gradually transitioned to greater use of military power and then had a tragic tactical stumble trying to arrest a warlord. The loss of 18 Americans caused national outrage, and eventually we pulled out. We experienced classic mission creep, without reconsidering the strategy or the means to achieve it.

In Libya, if the objective is humanitarian, then we would work with both sides and not get engaged in the matter of who wins. Just deliver relief supplies, treat the injured and let the Libyans settle it. But if we want to get rid of Gaddafi, a no-fly zone is unlikely to be sufficient — it is a slick way to slide down the slope to deeper intervention.

Determine the political endgame before intervening.

In Haiti in 1994, it was a matter of getting rid of the military junta that had forced out the democratically elected president and restoring a democratic government. We prepared and threatened an invasion, we used it as leverage in negotiations, and within four weeks of its start, President Jean-Bertrand Aristide was back in power.

But in Iraq in 2003, we failed to chart a clear path to democracy before taking action. So after we toppled Hussein, we lacked a ready alternative. Eight years later we’ve come a long way, but at a very high price.

In Libya, we don’t know who the rebels really are or how a legitimate government would be formed if Gaddafi were pushed out. Perhaps we will have a better sense when Secretary of State Hillary Rodham Clinton meets with rebel leaders, as she is scheduled to do this coming week. In a best-case scenario, there would be a constitutional convention, voter lists, political parties and internationally supervised free and fair elections. But there could also be a violent scramble for authority in which the most organized, secretive and vicious elements take over. We are not well-equipped to handle that kind of struggle. And once we intervene, Libya’s problems would become our responsibility.

Get U.S. public support, obtain diplomatic and legal authority, and get allies engaged

Offensive war is, in general, illegal. In the Persian Gulf War, Iraq’s actions in 1990 were a clear case of aggression; we obtained full U.N. support. We had a congressional resolution. And we enjoyed the overwhelming backing of our allies and Arab partners. They even paid most of the cost of Operation Desert Storm, to the tune of tens of billions of dollars. The resulting military action was widely hailed as a legitimate and moral victory.

In 1999 in Kosovo, the United States and NATO had a humanitarian U.N. resolution backing our actions. The American public was mostly unengaged, but NATO was able to wield its diplomatic power and the incremental use of force to compel Milosevic’s surrender. (The coup de grace was his indictment for war crimes by the International Criminal Tribunal on Yugoslavia.)

By contrast, going it alone, without substantial international legal and diplomatic support, is a recipe for trouble. Our haste and clumsiness going into Iraq in 2003 — without a compelling reason to intervene, in my view — has cost us dearly.

In Libya, Gaddafi has used and supported terrorism, murdered Americans and repressed his people for 40 years. The American public may want to see him go. But his current actions aren’t an attack on the United States or any other country. On what basis would we seek congressional support and international authorization to intervene in a civil war? Do we have the endorsement of the Arab League? A U.N. Security Council resolution?

Avoid U.S. and civilian casualties.

In Kosovo, NATO had the upper hand from the outset. We weren’t losing aircraft (we lost only twoin combat out of 36,000 sorties flown over 78 days); we never lost a soldier or airman in combat; and because we minimized innocent civilian casualties and the destruction of nonmilitary property, we maintained our moral authority.

But once Americans start dying, public tolerance for military action wanes sharply. We’ve seen it time and again, from the aborted attempt to rescue our hostages in Iran in 1980 to Afghanistan today. Intervening successfully isn’t so much a matter of how many troops and planes you use, it’s about mustering decisive power — military, diplomatic, legal, economic, moral — while avoiding the casualties and collateral damage that discredit the mission.

A no-fly zone in Libya may seem straightforward at first, but if Gaddafi continues to advance, the time will come for airstrikes, extended bombing and ground troops — a stretch for an already overcommitted force. A few unfortunate incidents can quash public support.

Once you decide to do it, get it over with.

Use decisive force – military, economic, diplomatic and legal. The longer an operation takes, the more can go wrong. In 1983, we went in with overwhelming force against an attempted communist takeover in Grenada. With 20,000 U.S. troops against 600 Cuban military engineers and some ill-trained locals, it was over in three days. The Cubans were out, the American students who had been held hostage were freed and casualties were minimal. Grenada transitioned to democracy.

The operation in Panama lasted about three weeks; the ground fight in the Gulf War only 100 hours. We pushed the limit in Kosovo with a 78-day air campaign, but fortunately, Milosevic ran out of options before NATO had to commit to planning an invasion.

Given these rules, what is the wisest course of action in Libya? To me, it seems we have no clear basis for action. Whatever resources we dedicate for a no-fly zone would probably be too little, too late. We would once again be committing our military to force regime change in a Muslim land, even though we can’t quite bring ourselves to say it. So let’s recognize that the basic requirements for successful intervention simply don’t exist, at least not yet: We don’t have a clearly stated objective, legal authority, committed international support or adequate on-the-scene military capabilities, and Libya’s politics hardly foreshadow a clear outcome.

We should have learned these lessons from our long history of intervention. We don’t need Libya to offer us a refresher course in past mistakes.

Wesley K. Clark, a retired Army general and NATO’s former supreme allied commander in Europe, is a senior fellow at the Burkle Center for International Relations at the University of California at Los Angeles.