BRITAIN had little choice but to break off diplomatic ties with Libya. Col. Muammar Qaddafi's unhearing response to British appeals - for access to the Libyan Embassy in London to question personnel about the shooting of a London policewoman among demonstrators outside the compound - could not be allowed to stand.
Britain's solution to the impasse over the incident was tempered, though not without its risks. Britain has ordered the Libyans to leave the embassy ''at the earliest possible moment,'' at the latest this Sunday. At that point diplomatic immunity will cease for the 20 or 30 Libyans in the embassy. Presumably, if the embassy empties before then, the party guilty for the shooting will escape punishment in London. In Libya, the 8,000 or so British subjects must consider their own safety. The British ambassador's family has already begun packing.
Diplomatic immunity cannot be absolute. Actions like Britain's were anticipated in the 1961 convention which Britain and Libya both signed.
Diplomatic missions are to some degree hostage to the host country. There is often some tension between guest and host. Guests and their personnel need some protection against harassment by the host country. Host countries must make a calculation, at the time of some legal infraction or other unwanted action, whether the price of immunity is too high. When the United States Embassy in Moscow took in the Pentecostal families for sanctuary, the greater importance of maintaining US-Soviet relations obviously had to prevail. In this instance, the price of a free hand to the Libyans to fire upon others in Britain was too much for London to pay.
Severing diplomatic ties is generally done with regret. The United States in 1981 found it could no longer tolerate Libyan misuse of its mission for violence in America. Since April 1982 Libyan oil sales to the US have been halted, by presidential order, driving Libya into bartering arrangements with other countries to keep crude oil sales moving. Washington has been sending Qaddafi messages that there are limits to his mischiefmaking.
What impact the British response will have on Colonel Qaddafi is unknown. The Libyan leader is at best an enigma to outsiders. There appears to be no way to measure the level of discontent within Libya to his rule. But the hanging of two youths by fellow students in Tripoli a week ago, which sparked the demonstration in London, indicates the level of irrationality inside Libya.
What the British must do is act according to their own sense of the law, minimizing any jeopardy to British civilians abroad. At the least, one hopes Colonel Qaddafi can honor the appropriate mutual diplomatic exodus from Tripoli and London.