London — Sounding blunter by the minute prime Minister Margaret Thatcher is hardening the tough line on the Falklands war that she intends to present to President Reagan and other leaders at the summit meeting in Versailles.
At the same time, she has also hinted at a possible United States role in guaranteeing peace after the fighting is over and has said she expects the US to agree if asked.
Britain, she said, in a television interview June 2, agreed to contribute to the multilateral force in the Sinai because it was a way to bring peace. She added ''I am sure we will have the same response''--words taken here to mean that she would expect the US to contribute to a Falklands force if Britain should request it.
She gave no further details. However, it is expected here that President Reagan will be wary of any commitment that could lead to deeper criticism of the US by Latin American countries.
With British forces shelling Port Stanley and poised on the high ground above the town for a final assault, the prime minister publicly ruled out any thought of British ''magnanimity.''
Asked her response to advice that she should now be magnanimous, she replied:
''It is not a word I use in connection with the battle on the Falklands. . . to give something back in these circumstances to an invader, an aggressor, and military dictatorship. . . would not be magnanimity, it would be treachery and betrayal of our own people.''
This was a clear indication that the prime minister will reject any pressure on her from Mr. Reagan or any other leaders at Versailles to allow Argentina more time to reach a negotiated solution.
Mrs. Thatcher was expected to use the summit in part as a forum in which to lobby hard for continued support from other nations--including strict adherence to European Community trade sanctions. She is concerned to keep the support--both diplomatic and logistical--of the United States, but she is not prepared to stop her military advance on Port Stanley or yield to Argentina in any way.
She was asked what she would say to Mr. Reagan if he asked for ''another chance'' to persuade Argentina to withdraw. She replied she did not understand the words ''another chance.''
Britain had been waiting for more than seven weeks for Argentina to obey United Nations Security Council Resolution 502 and withdraw. It was, she said, only too easy for Buenos Aires to ask for more time.
She insisted she was not trying to humiliate anyone: ''I am just trying to repossess islands which are British sovereign territory. That is not humiliation. That is liberty, justice, and democracy.''
A cease-fire could now come only if Argentina promised to withdraw within a definite time period--say 10 to 14 days. But she did not think it likely that a battle for Port Stanley could be avoided.
Meanwhile, Defense Ministry sources in London indicated that Port Stanley was defended by 2,000 Argentine Navy and Airforce troops and 5,000 conscripts.
British forces were bringing up supplies and ammunition and were sending out reconnaissance patrols.
The sources said that Britain would be ''extraordinarly fortunate'' if Argentina gives up before the end of next week. Britain believes large numbers of Argentine forces will surrender quickly but some will continue to resist.
The Defense Ministry announced June 2 that Britain had lost two Harrier jets in raids on Port Stanley, bringing total Harrier losses to eight out of a complement of 40.
British diplomacy has hardened: The prime minister insists British rule must be restored on the Falklands and the islanders given a lengthy period--which could be up to 12 months--to decide how they want to be governed.