No American military action is planned against Libya, President Reagan made clear at his Tuesday press conference. A wise decision, but its wisdom is diminished by the week of empty talk and useless naval maneuvers that preceded it. Empty threats -- here today, withdrawn tomorrow -- give gunboat diplomacy a bad name. This time they served only to increase Col. Muammar Qaddafi's stature and induce the Arab League and the Islamic Conference to rally round him. Even President Hosni Mubarak of Egypt, for whose overthrow Qaddafi calls weekly, felt compelled to warn the United States away.

There is a time and place for military retaliation, and this was not it. After all, whom to hit? Abu Nidal? We won't find him: the rat burrows deep in the sand, so deep that until a year ago he was presumed dead. Qaddafi? You don't send out your Air Force to kill a head of state. Not even Syrian President Hafez Assad, who in 1982 killed 10,000 to 20,000 of his own people putting down the Hama revolt, does that. When he wanted the president-elect of Lebanon, Bashir Gemayel, disposed of, he didn't send a plane with Syrian markings to drop a bomb on Gemayel's head. He sent his agents. We have agents too.

Not that the United States should want to kill Qaddafi. That's against American law, and we don't want to break any laws. Overthrowing him is another matter. There are plenty of Libyans eager to do so who could use our help. Whether Qaddafi survives an overthrow should be a matter of utmost indifference to us. (If he did survive, he would perhaps find accommodation with Idi Amin at his guest quarters in Saudi Arabia.)

The Europeans, for once, seemed shocked enough by the airport msacres to countenance something being done -- by the United States. As Americans were shocked enough to want to see something done -- by Israel. Israel correctly said no, as did Reagan.

Imagine there were an American air strike. We could count on European statesmen quickly to repress their satisfaction and issue, with typical mendacity, pious denunciations. One doesn't have to launch an air strike to tap this ample vein of scrupulousness. A simple capture of terrorists will do. David Owen, leader of Britain's Social Democratic party, on the U.S. seizure of the Achille Lauro hijackers: "International terrorism, abhorrent as it is, cannot justify states violating international law, whatever the provocation, whatever the frustration." France refused to comment on the American capture. It needed first to examine "certain elements" of the act pertaining to its international legality, said an official spokesman, exactly three months after France blew up the Rainbow Warrior in Auckland harbor.

President Reagan was also right to cut all remaining ties between the United States and Libya. But he then implored the allies to do likewise. The plea was both pointless and degrading. He knows they will turn him down. After the TWA hijack-murder last June, he asked the allies to join in boycotting Beirut airport, a measure requiring no more than an ounce of respect for the United States and no courage at all. The response was, as one American official put it, a "deafening silence."

Europe will do nothing to jeopardize pan-Arab favor or Libyan trade. For all the president's communications skills, Eurocowardice will not yield to trans-Atlantic chiding. I suggest, therefore, the use of a two-by-four: the State Department travel advisory.

We slapped one on Greece last June after the TWA hijacking out of Athens (and the Greek government's craven release, before the plane had even finished its journey, of the one captured terrorist). No coercion. No threats. Just advice to American tourists: Athens is unsafe. The effect on the Greek tourist industry was gratifyingly catastrophic. Within days the Greek government complained loudly. Within weeks it had overhauled security at Athens airport.

The use of Libyan embassies and diplomatic pouches for storing and transferring weapons is no secret to any European government. Therefore, let the United States announce that it will issue a travel advisory for any country in which 1)Libyan-supported terrorists attack Americans and 2)the host country allows Libyan embassies and trade missions to remain open.

It is a reasonable precautionary measure: a country in which Libyans can ferry arms and hide terrorists is a country unsafe for Americans. Beefing up airport security will no longer do. No airport can be made airtight. Disrupting the terrorists' European infrastructure is essential. The Libyan connection is the place to start.

Start with Rome and Vienna. Declare them unsafe unl the host countries begin steps to cut diplomatic and trade relations with Libya. If this security measure is denounced as a disguised form of political pressure, let the State Department issue a denial.

This strategy is not only more dignified than begging Europe to isolate Libya. It is also more likely to work.

An old postscript: In his Taking Exception (op-ed, Dec. 24), Rep. Stephen Solarz (D-N.Y.) denies the "Solarz Doctrine" -- that he will support only faraway insurgencies -- thus: He supports Afghan but not Angolan rebels, and Kabul is closer to Washington than is Luanda. I hope that before his next flight to Kabul, Solarz consults the Air Distances Manual of the International Air Transport Association. If he takes only enough fuel for a Luanda-distance trip, he is in for a premature landing and a 290-mile walk. Kabul is indeed 6,924 miles from Washington. But Luanda is 6,634, not 7,008 as Solarz imagines.