IT IS THREE MONTHS since President Reagan sent planes against Libya, and note is being taken -- with crossed fingers -- of the subdued policy of Col. Moammar Gadhafi. No new acts of terrorism have been attributed to him. Some suggest that his murderers have been taking a break or otherwise lying low before resuming their deadly trade. Another line of speculation, bolstered by reports of Col. Gadhafi's personal deterioration, is that the American attack may have broken his invigorating assumption that his deeds were cost-free.

All this is very interesting, but what is very important is that the interval since the April 15 raid has been put to some good effect by the Western allies. Most of them needed the shock. The example of decisiveness, the undeniable precision of the intelligence, the subsequent demonstration of Libya's isolation and, not least, the fall in tourism: these elements have put new vigor into European responses. Even Greece, the one ally that shrank from its antiterrorist commitments, has been finding its own ways to reduce the Libyan presence (in its outsize Athens embassy, Libya had 19 "cultural attache's") and to screen more effectively the comings and goings of Col. Gadhafi's minions.

Beyond the police and intelligence front, attention fixes on the courts. Their basic mission is to serve justice, but they are also asked to serve governments that are under heavy pressure either to reclaim hostages or otherwise to propitiate the state or organizational sponsors of terrorism. The one mission drives courts and other official agencies to be tough, and the other pushes them to be lenient. The Italians have just given substantial sentences -- though not substantial enough for everyone's tastes -- to the Achille Lauro killers. Spain, apparently for exchange purposes, has freed two Shiites serving 23-year sentences for murder. In France the force of public opinion in behalf of the country's remaining hostages taken in Lebanon seems to be inclining the government to consider releasing a terrorist, George Abdallah, accused in the murder of an American military attache' and an Israeli diplomat.

Each situation is distinctive, but it is worth noting the disposition evident in London. Britain needs no more collisions with Arab states. Nonetheless, even while French officials receive Syria's vice president, British authorities have directly implicated the Syrian government in the foiled plot -- in the incredibly foolhardy plan, one that could have triggered a major war -- to destroy an Israeli airliner in April. Since then, President Hafez Assad seems to have had his killers on a short leash too.