Gen. Leopoldo Galtieri, the latest heir of Juan Peron, is relying on a stale and comic caricature of British "colonialism" to sell his country's sneak seizure of the Falkland Islands.

George Orwell once recalled, from the boys' weekly papers of his youth, just such a caricature: "The comic foreigners are jabbering and gesticulating, but the grim, gray battleships of the British fleet are steaming up the Channel and at the outposts of empire the monocled Englishmen are holding the natives at bay."

Some Americans are old enough to remember something like it, when the schoolroom maps showed great splotches of British imperial pink, from Barbados to Bombay.

But as justification for the use of force to overbear the wishes of the Falkland Islanders, Galtieri's caricature is a thin fig leaf. It failed last weekend at the U.N. Security Council, ordinarily eager to oblige any bogus assailant of "colonialism." It seems equally likely to fail with the Organization of American States, where a certain collegial sympathy is dampened by the awareness of other festering territorial disputes that could break out into fighting.

It is odd, perhaps even a bit anachronistic at first glance, that Britain should mobilize its largest armada in four decades to reassert a "dominion over palm and pine" that in this case involves no trees at all but 700,000 sheep, 38 sheep-shearing stations and 1,800 isolated English-speaking people.

But a vital principle, still important to law-abiding peoples, is under rude assault: that what the British government has carefully called "administration" cannot be altered by force.

The Falkland dispute is one of the oldest on earth, if you count Britain's clashes with Spain. It is a bit like the endless lawsuit in Charles Dickens into which generations had been born, from which generations had died out, and of which no one recalled the exact origins.

There was a remarkably similar tiff just before the American Revolution. A Spanish force raided the British outpost at Port Egmont in the Falklands, forcing the Britons to put to sea in a rudderless sailing ship--a humiliation that also caused the resignation of a foreign secretary and an outcry over the state of the Royal Navy.

But that was before mass opinion (or oil) became a concern, and 18th century diplomats finessed the dispute. After a suitable exchange of apologies, both nations by quiet agreement withdrew their competing outposts.

It is at least possible, if not probable, that the present clash will end as quietly. By the time the carrier Invincible and its 33 sister ships reach the South Atlantic, tempers in London and Buenos Aires could have cooled and second thoughts about war arisen.

But Argentina will have to give first, for Britain is determined, as it must be, that the English-speaking Falklanders choose their own fate and affiliation. At issue is not so much a disputed claim to abstract "sovereignty" as the principle of negotiated self- determination on which Britain's peaceful dissolution of the empire has been based since World War II.

Self-determination is vital. The world is crisscrossed by disputed boundaries and contested claims of nationality and sovereignty, now as ever. And as the bitter dispute over the U.S. treaty with Panama illustrates, nothing stirs more anger than a quarrel over sovereignty. Every recourse to arms is a gain for the latent forces of anarchy.

The Argentine regime has accompanied its assault on imaginary British "colonialism" with grandiose talk about the gentlemanly resolution of disputes. The invading Argentine general was offended that the British governor refused to shake hands. It was, he said, "ungentlemanly."

This fake chivalry, like the pretense that the British are maintaining a "colony" in the Falklands, is a facade for the high-handed use of force. The Argentine dictatorship is promising to be nice to the islanders. But in view of Argentina's habitual treatment of its own citizens, that is no consolation.

Argentina last figured large in the U.S. news when the exiled Argentine editor, Jacobo Timerman, stopped here en route to Israel to report on Argentina's systematic assault on civil liberties. Timerman pictured a regime so far sunk in paranoia as to regard Freud and Einstein as a dire threat to Argentina's survival and to suspect a plot to set up a Jewish state in Patagonia. Thousands of Argentinians who took a more rational view have simply disappeared.

In reaching a civilized accord with such a crowd, the diplomats will have their work cut out.