London — The British diplomatic mood is combative as President Reagan visits London.
Britain believes itself the aggrieved party in the Falklands war, and officials have little patience with any differing view.
Apart from the Falklands issue, Mr. Reagan comes to Britain at a time of steady and close relations. Britain, like other Europeans, wants United States interest rates to fall, but Mrs. Thatcher is ideologically in tune with Reagan economics and hopes his attacks on inflation will succeed.
Criticism on economic issues, and impatience over US budget wrangling, are also muted.
But it is Britain's tough mood over the Falklands that could quickly have an impact on the US. Britain is putting heavy pressure on the US to lend soldiers to a peace-keeping force on the Falklands.
The pressure has been piled on Mr. Reagan by an eager Prime Minister Margaret Thatcher in Versailles. It will continue here at meetings June 7, 8, and 9 and at the June 10 NATO summit in Bonn.
Sources here expect Mr. Reagan to agree in the same way that Mrs. Thatcher said ''yes'' to him when he asked her to contribute to the peace-keeping force in the Sinai.
But there are indications that the Reagan team has deep misgivings about British strategy in general. This seemed evident during the Security Council vote June 4, when on the orders of US Secretary of State Alexander M. Haig Jr. the US broke with Britain by announcing that it should have abstained rather than casting a veto along with London.
This shift is said to have angered Mrs. Thatcher, who vetoed the resolution because it did not specifically link a cease-fire with an Argentine withdrawal.
Now comes another report that suggests the US is cool to the multinational force idea as well.
A Washington correspondent for Independent Television News (ITN) quoted White House sources June 6 as saying that the US would take part in a multinational force only if it administered the islands as well as kept the peace.
The US plan reportedly would have the United Kingdom task force go back to the North Atlantic, leaving administration of the Falklands in the hands of the UK, the US, Brazil, and Jamaica. The US reportedly wants talks on the future of the Falklands to begin within three to six months. They are to include Argentina.
But these ideas were immediately rejected by a member of the British war Cabinet June 6. Tory party chairman Cecil Parkinson said that a multinational administration was simply not acceptable. The US, he said, had not yet realized how tough British opinion had become since the fighting began.
The British view, obtained in interviews from closely informed sources here, goes like this:
Britain is no longer able or willing to allow Argentina any form of sovereignty over the Falklands in the foreseeable future. Argentina had its chance. It could have accepted British concessions a month ago, especially those of May 17. But it rejected them, and now British lives have been lost, ships sunk, and planes downed.
Britain notes that Argentina has allowed its forces on the Falklands to shoot at British forces after the Argentines sent out a white flag. Britain also claims Argentina prepared napalm bombs and locked British residents of Goose Green in an assembly hall for days.
''The British public simply will not accept concessions now, after the fighting and the losses,'' a diplomatic source said. ''It would be regarded as a sellout, and it is simply not on.''
Mrs. Thatcher makes it clear in public and in private that Britain has fought in the Falklands for what the US Constitution also enshrines: liberty, democracy , and the rule of law. She calls US support for Britain ''splendid''--but she also makes it clear that she wants Mr. Reagan to do even more.
The biggest long-term loser in the Falklands war could be the US.
Mr. Reagan's dilemma is that if he agrees to have US troops serve alongside those from other nations in a peace-keeping force, it will please his NATO ally Britain, but he will offend many in Congress and in Latin America. They probably will see even one US soldier on the Falklands, in whatever capacity, as a virtual enforcement of colonial rule. The Soviet Union may attempt to turn the situation to its advantage through propaganda.
The US undoubtedly will be seen by a number of Latin American countries as having gone too far, and certainly way beyond supplying Britain with Sidewinder air-to-air missiles, other ammunition, fuel, and in-flight refueling.
In a notable hardening of her diplomatic stand, Mrs. Thatcher said on television June 2, ''I cannot myself see a role in anything relating to sovereignty for the Argentines on the Falkland Islands. . . .'' She said the islanders would reject it.
So the islands are, in the British view, to be made ready to stand on their own feet. Their economy is to be broadened beyond sheep raising. Oil and gas deposits remain to be developed. Giant reserves of krill, a small shrimp-like fish rich in protein, could be tapped. Wildlife and even tourism offer long-term possibilities.
But before any of this can be done, Britain says the Falklands must be made physically secure from any future attacks from Argentina.