London — When the dust of the London embassy siege settles, Britain will look to the international community to support it in moves to tighten up the Vienna Convention on Diplomatic Conduct.
As London police awaited the departure of Libyans from their so-called people's bureau, following the British decision at the weekend to break diplomatic relations, the broader implications of the crisis were already being weighed by senior members of Prime Minister Margaret Thatcher's government.
Amendment or at least substantial reclarification of the 1961 convention is considered essential, with emphasis on the abuse of diplomatic premises and the diplomatic bag for terrorism and other illegal activities.
Initially, Britain will approach its partners in the European Community for their views on this question. An approach to the United Nations Secretary-General, with a request for a review of the Vienna Convention, will probably follow later.
Members of Parliament of all parties are pressing the government to reconsider the immunity from entry and search enjoyed by foreign embassies in London.
Libya's determined application of the immunity principle prevented police from going into the embassy from which shots were fired last week, killing a policewoman and injuring 10 anti-Qaddafi Libyan protesters.
This produced a stalemate which Britain decided to end by breaking relations with Libya and ordering all people in the embassy to return to Libya within a week.
The British expulsion move followed six days of intensive, secret, and in the end fruitless negotiations between London and Tripoli. It was after Colonel Qaddafi went on television and accused Britain of causing the crisis that Mrs. Thatcher and her advisers decided a diplomatic break was the only honorable course open.
After the decision Sunday, Libyans inside the bureau indicated that they were in no hurry to leave and would probably stay in the building until a few hours before the deadline of midnight, April 29.
At that point, the building will lose its immunity and police will be able to enter. If the occupants have left by then, they will enjoy safe conduct back to Libya under a British guarantee that will apply to accredited diplomats and revolutionary students who claimed to have taken over the embassy last February.
Two aspects of the affair are expected to cause embarrassment to the Thatcher government. The murderer of the British constable will be able to go home free, and the Libyan diplomatic bag will not be searched or X-rayed.
If, as is widely believed, there are guns and explosives inside the embassy, they will probably be returned to Libya in this way. That would be a further abuse of the Vienna Convention.
There were signs that Britain's expulsion order caught Colonel Qaddafi unawares. Observers in Tripoli said he had not expected his embassy staff in London to be given the order of the boot. (UPI reported Monday that Libya had threatened to increase support for Irish Republican Army terrorism and take other ''revolutionary action'' against Britain if it does not extradite the ''criminals'' that Libya claims attacked the London embassy.)