COL. MUAMMAR QADDAFI is having some success in his latest effort to subvert the one country in Africa and the Middle East that remains most vulnerable to his malign hand. The place is, of course, Chad, whose proximity to Libya, poverty and ethnic diversity have made the former French colony a fertile field for foreign intervention for most of its two decades of nominal independence. This time around, Libyan aircraft and artillery seem to have allowed Chadian rebels to sweep government forces from the northern town of Faya Largeau. So now what?

The empire-minded Qaddafi has done something nasty that troubles many Africans of the region and embarrasses their foreign patrons, including France and the United States. The mischief he has done, however, should not be treated in a manner to make of it a myth. Faya Largeau is not Stalingrad. This was a small skirmish in a remote place and, as we say, it was far from the first of its type. Libya's forces won out not because they represent some irresistible green tide--Col. Qaddafi colors his revolution green--but because in the ebb and flow of military action in the African desert, they had an advantage at this time and place. Politically, the Chadian figure supported by Libya appears to be no more than a warlord on the make--in other words, a politician familiar to hard-to-govern, poorly governed, little-governed Chad.

One evident result of the Libyan pounce on Faya Largeau is to mobilize a certain coalition of forces that are prepared for their separate local or strategic reasons to take some kind of stand against the further depredations of Col. Qaddafi. The coalition was ineffective in the first stage, but it is in a position to make a difference in the next. It would be surprising if President Hissene Habre's regional patrons in Egypt and Sudan, both themselves targets of Libyan subversion, were not more ready now. French paratroopers, strongly armed, are finally and belatedly in place in the capital of Chad in the south. Other Africans are also aroused. The United States no longer appears to be awkwardly out in front of the anti-Qaddafi elements.

President Reagan had it about right in his remarks on the Chad crisis the other day. He steered clear of rhetoric whose effect in the past has been to paint Col. Qaddafi as a menace so powerful, radical and Soviet-inspired as virtually to cry for a direct American intervention against him. Instead, he emphasized the poor quality of the information about Chad available to Washington, the clear implication being the need to proceed cautiously. Chad, he observed, is historically in France's sphere of interest --another piece of sober distancing. "I don't see any situation that would call for military intervention by the United States there," he said.

Chad finds the United States in the usual difficult spot. The African country is not important to Americans in any conventional or traditional way, yet it is part of the business of being a great power to do what can be done to keep local or regional bullies from pushing unoffending countries around. Mr. Reagan caught the spirit of this dilemma when he said it was not the American role to play world policeman, and, in the same breath, observed that threats to American security can arise worldwide. To combine the necessary restraint and responsibility takes good judgment, good company and, not least, good luck.