What is the morality of war?
How triumphant should the British be at their ''victory'' over another nation , Argentina, which is also Christian?
A significant segment of the British establishment is debating in private and in public just how a democratic society such as Britain ought to look back on the Falklands war. And at the center of the current tug of war here is a major church service on the war to be held July 26 in St. Paul's Cathedral.
Officially the service, to be attended by members of the royal family, Prime Minister Margaret Thatcher, the Cabinet, and other leading members of the establishment, is billed as one of ''thanksgiving, remembrance, and reconciliation.'' From the moment the service was announced, however, it has been controversial. Its final form is not yet clear.
The prime minister reacted strongly against a proposal that prayers in the Spanish language should be included, and made her displeasure clear to the church hierarchy. To her, and to such Cabinet ministers as Defense Secretary John Nott, having Spanish spoken in St. Paul's would contravene what the war was fought for in the first place - restoring sovereignty over territory tha had been illegally invaded by a Spanish-speaking military junta.
During the war, Mrs. Thatcher and a majority of British people felt the fighting was justified as a necessary means of defending the principles of sovereignty, self-determination, and the rule of law.
Senior Cabinet members do not even want the brief remarks of some of the more pacifistic figures invited to take part in the service printed as part of the program - but the Church of England is likely to go ahead and print them anyway.
The church hierarchy recognizes that it must be an ecumenical occasion, and that Cardinal Basil Hume, head of the Roman Catholic Church in Britain, should attend and take part. But the cardinal is extremely sensitive about Argentine opinion, and was at first reported to be opposed to participation by military chaplains. He is understood to have dropped his objections in recent days.
Many Britons, besides the prime minister and including deeply troubled members of the Anglican Church, have been letting their own opinions be known in no uncertain manner.
The Archbishops of Canterbury and York have asked for prayers for the relatives of those killed on both sides. A leading Anglican intellectual, Martin Dent of the political department of the University of Keele, suggested that ''it is altogether fitting and proper for us to remember the dead on both sides before God who is Lord of all.''
The Bishop of Lincoln asked: ''Thanksgiving for what?. . . . For restored peace, yes; for exceptional efficiency, endurance, and heroism of the armed forces, yes indeed; for the general steadfastness and courage of those in authority, once committed, yes. But, pray God, not in any nationalistic spirit, for winning a war.''
A Roman Catholic priest, the Rev. Barnabas Lindars, wrote to the London Times from Manchester saying that if the prime minister objected to the Lord's Prayer in Spanish, perhaps she would agree to a prayer attributed to St. Francis, ''Lord, make me an instrument of thy peace.''
Giving an informed Roman Catholic viewpoint, Clifford Longley, religious affairs correspondent of the Times, said British churches now had a remarkable opportunity to articulate a new sense of ''national hope and purpose.''
He called for the St. Paul's service to celebrate peace rather than war, and reconciliation as well. The word, as used by Pope John Paul II during his recent visit to Britain, indicated a brotherhood between men that did not stop at ''the limits of national identity,'' Mr. Longley wrote.
cl11 He went on: ''As reconciliation between nations has manifestly not been achieved by the South Atlantic operation, that concept sets a severe brake on any tone of self-congratulation: at least half the job has not yet been done.
''There are other questions the nation is ready for, such as how Britain's participation in the international arms trade could possibly be described as reconciliatory, and whether a peace sustained by NATO and nuclear deterrence is really peace at all. Praising God and passing the ammunition has now outlived its time.''