London ? At the height of bloodletting in Northern Ireland, the British government considered trying to end the sectarian conflict by forcibly moving hundreds of thousands of Catholics to the Irish Republic, according to records released Wednesday.

But the top secret contingency plan — dated July 23, 1972 — was rejected out of concern it would not work unless the government was prepared to be “completely ruthless” in carrying it out, and that it would provoke outrage at home and abroad, especially in the United States.

“We do not believe that the government would be able to obtain the support of public opinion in Great Britain for the drastic actions that we consider in this paper,” the newly declassified document said.

“Any faint hope of success must be set against the implications of a course which would demonstrate to the world that (the government) was unable to bring about the peaceful solution of problems save by expelling large numbers of its own citizens and doing so on a religious basis,” the document added.

It is the first indication that Britain once considered using a method that came to be known as “ethnic cleansing,” a strategy Britain, among many nations, denounced when Serbs used it against Muslims and ethnic Albanians during the Balkan wars of the 1990s.

The plan came to light in a batch of formerly confidential papers declassified after 30 years and released by Britain’s Public Record Office. The plan is contained in a report commissioned by the government of Prime Minister Edward Heath to prepare for a time when Britain was on the verge “of losing control” in Northern Ireland, the document says.

Almost 500 people were killed in 1972, more than any year since. On Jan. 30 of that year — now known as “Bloody Sunday” — British soldiers shot and killed 13 unarmed Catholic protesters in Londonderry.