London — A new battle over the Falklands has been opened - this one over the role the United States will play in the islands after the British and Argentines have finished fighting.
It is a diplomatic rather than military struggle, starting even before the final British assault on Port Stanley had been completed. And Prime Minister Margaret Thatcher may well be asking for more than the Reagan administration is willing to offer.
The prime minister opened the new diplomatic struggle shortly before the Versailles summit by serving notice to US and British correspondents that she was thinking of a multinational peace force to secure a retaken Falklands from future Argentine attacks.
Insisting that Britain alone would continue to govern the Falklands and would gradually move them toward independence, she suggested that the US should contribute men to a peace force, along with other countries. Britain, she said, had agreed to a request from Mr. Reagan to send troops to the peace-keeping force in the Sinai. She added repeatedly that she felt that Mr. Reagan could do no less for her, if he was asked.
When they met at Versailles, the prime minister bombarded the President with her ideas. Here in London, she relied more on a series of interviews with US television networks late June 8, than she did on her only business meeting with him - 45 minutes at breakfast June 8 before the Reagan party left for Bonn.
By the time Mr. Reagan arrived in London, Mrs. Thatcher was sensing that the United States might well be cool to the multinational force idea.
Secretary of State Alexander M. Haig Jr. diverged from the British diplomatic position at the UN, by ordering the US delegate to abstain on, rather than to veto, a Security Council cease-fire resolution which Britain strongly opposed.
Also, news reports from Washington indicated US doubts that Britain could hold onto the Falklands indefinitely, and US concern that Washington could lose even more support in Latin America by contributing soldiers to a peace force.
The reports suggested that the US might take part in a multinational administration and that Argentina should participate in talks on the Falklands future within six months.
Britain's answering salvo to this suggested coolness came June 6 when a member of the war cabinet, Conservative Party Chairman Cecil Parkinson, said the ideas were not acceptable and that Argentina could have no part in any sovereignty over the Falklands in the future.
Speculation broke out in London that Mrs. Thatcher was ready to abandon her idea of involving US forces. The London Times of June 8 put on its front page an article attributed to ''sources close to the prime minister'' and headlined ''Hopes Fade for US Occupation.''
The battle continued late June 8, when government sources here privately dismissed that report and denied that Mrs. Thatcher had asked for any formal US commitment.
It seems clear, however, that while it was too early for Britain to ask the US to commit itself, the prime minister had actively pursued the idea. At her breakfast meeting with Mr. Reagan June 8, she touched on the Falklands only briefly, and concentrated on the Israeli invasion of Lebanon and the NATO meeting in Bonn. But before leaving for Bonn later in the day, she told US networks that she was indeed looking to the United States for assistance as well as for diplomatic support.
She said that the most immediate need for help could be for US supplies to help take care of large numbers of Argentine prisoners. She was expecting that those prisoners would be taken in the final assault on Port Stanley which had not taken place at time of writing.
In the longer term, she was careful to say that the need for a multinational peace force was not imminent.
Britain planned to return the islanders to their homes and to repair damage caused by the war.
But she was adament that Argentina had lost any possibility of gaining any sovereignty over the islands at any time in the future.
The islanders themselves must be allowed to determine their own future, and she had no doubt that the Argentine occupation that began on April 2 would cause the island population to turn wholeheartedly to Britain.
The British problem will be to defend the Falklands, perhaps for a long period, against an Argentina thirsting for revenge. She told US television interviewers that her government was prepared to pay the costs of defending the islands; ''freedom is expensive to defend,'' she said. ''It is worth defending.''
Britain would extend the airstrip at Port Stanley so that it would take large aircraft. If necessary, Britain would install Rapier anti-aircraft missiles around the airstrip and would keep some submarines and ships in the area.
But she stressed her hope for US help. The Falklands, she said, were strategically important: ''Even now, you know. . .some very big oil tankers have to go around Cape Horn to get to Alaska. . .. (The islands) are to some extent also the gateway to the Antarctic which will be progressively more important in resource terms to the world as a whole.''
The next stage in the new battle of the Falklands will be played out in the United States, whose government has to decide just how much support to give, in light of its own diplomatic challenges in the hemisphere.