For the moment at least, the talking is over, and force is replacing diplomacy. Britain says it has no choice.
In dramatic scenes in the House of Commons chamber in London, Prime Minister Margaret Thatcher has signaled an end to seven weeks of intense worldwide negotiations, and a period of open naval, land, and air warfare in the South Atlantic.
Britain is now finally launched on its most dangerous foreign policy strategy since its attempted invasion of Suez in 1956 and one of its riskiest since World War II, taking place at the end of a supply line reaching 8,000 miles to the other end of the world.
Also caught up in the escalating crisis is the NATO alliance, the United States and its relations with Latin America, potential Soviet gains there, and the prayers for peace of millions of people around the earth.
Britain faces the prospect of losses of men that could prove to be heavy, but insists that its cause is just, and as Mrs. Thatcher puts it, that its forces are defending democracy and freedom.
In ringing terms, the prime minister gave notice to Buenos Aires May 20 that the patience of her government was at an end. Essentially, she used her speech in the House, which opened a general debate on the Falklands, to give Britain's rationale for launching an invasion to regain the islands.
Seven sets of peace proposals since April 2, she said, had revealed an Argentina guilty of ''obduracy,'' ''deception,'' ''delay,'' and ''procrastination.''
Using some of the toughest language heard so far in London, she said any further talks would show that Argentina would simply be using the same tactics.
In a move immediately challenged by opposition speakers, she said flatly that Britain had withdrawn all concessions made so far. Argentina, she added, had not only rejected the latest British proposals of May 17, but had actually hardened its demands.
The prime minister went even further. She cast strong doubt over the newest efforts of UN Secretary-General Javier Perez de Cuellar to bridge the gap between the two sides by offering an aide-memoire listing points of agreement and ways of bridging areas of disagreement.
Several of the points made, she said, did not reflect either British or Argentine views with complete accuracy.
The first hint of the Thatcher government's adamant stand came when it broke with diplomatic practice and published May 20 its own latest proposals along with Argentina's reply, just received here. The unusual publication had three major aims:
1. To underscore London's almost complete distrust of the Argentine junta.
2. To retain as much support around the world as possible for Britain, given its clear intention of resorting to military force.
3. To persuade the British public here at home that the government had done all it could to try for peace.
By ending her opening statement to the House with the words that ''difficult days'' lay ahead, she left Britain convinced that it was only a matter of hours before news would come of a British naval and marine assault on the West Falkland Island.
While her fighting words were greeted with cheers by Conservative members, Labour opposition leader Michael Foot urged her or Foreign Secretary Francis Pym to fly immediately to New York to talk to Perez de Cuellar. Parliamentary leader of the Social Democrats, David Owen, himself a former Labour foreign secretary, questioned the withdrawal of all British concessions, and argued that Mrs. Thatcher should allow the Argentines to accept them under force of arms.
Left-wing worries came from Labour member of Parliament from Pontypool, Wales , Leo Abse, who said Britain would not be able to retain control of the islands indefinitely. Mrs. Thatcher, he said, should show more patience.
Mrs. Thatcher insisted she had not compromised basic principles in her concessions before May 20. She had preserved the concepts that ''aggression must not be allowed to succeed, international law must be upheld, sovereignty cannot be changed by invasion, and the liberty of the Falkland islanders must be restored.''
Britain's prime minister said that Argentine terms were ''manifestly impossible'' for Britain to accept.