THE ADMINISTRATION'S announcement once the TWA hostages were free that it would seek to "isolate" the Beirut airport produced some predictable responses. Those who seek forceful retaliation have deplored it as a mere gesture, a sign of weakness. Many Lebanese have also deplored it, as an overreaction that unfairly stigmatizes them and that will hurt their country but miss the terrorists -- it may even play into the hands of factions who have their own political reasons for isolating Lebanon.

Prime Minister Rashid Karami said that Lebanon "is all hijacked, as President Reagan knows." He said his country "has been the cradle of civilization, and if any power is to blame for the state of violence prevailing here . . . it is the United States. Of what is Lebanon guilty, that it is treated in this manner?"

Lebanon, of course, is not "guilty." It is a victim, not a criminal, among nations. It is, as its government says, the theater and not the agent of terrorism. Yet the Reagan administration is proceeding down the right track. The isolation of Beirut airport -- actually, it will be the further isolation of a facility whose use is already much restricted -- is not a complete or satisfying response to the hijacking. It is not offered as that. But it does seem to us to provide some of those who have power on the ground -- Nabih Berri, for instance, and the Syrians -- with an extra incentive to limit at least this one form of terrorism. It does not entail the unwise use of force.

The administration is asking other governments to join it in barring flights to and from the Beirut airport, including flights by Lebanon's Middle East Airlines, which after the civil service is one of the country's largest employers. Not all other countries may formally join -- the French own part of the airline -- but some surely will. Secretary of State George Shultz says the purpose is to put the airport off limits "until the people of Beirut put terrorists off limits." At least it's worth a test; that much is fair. And the purpose is as much precautionary as retaliatory. An airport should be safe to be sanctioned.

When Flight 847 was hijacked from Athens, the administration also put pressure on Greece, warning Americans away from the airport there. The Greeks complained bitterly at having been singled out, and agreed quickly to step up security at the airport. Pressure is not the single solution to the hijacking problem. But it can help.