AMID THE rising emotions of the Falkland crisis two weeks ago, Argentina arrested three British newspapermen for espionage. Unfortunately, the Argentine authorities are now compounding the original mistake by refusing to release them. It is a disquieting exception to the civility that both Britain and Argentina have observed so far in dealing with each other's citizens.

The three--Ian Mather and Tony Prime of the Observer, and Simon Winchester of the Sunday Times-- were arrested in Tierra del Fuego, at the southern tip of the country. But their continued detention seems to involve more than the anxieties of isolated provincial officials. According to the Observer, they were immediately flown 1,400 miles north to Buenos Aires by the naval intelligence service, then flown back to the province for a hearing that ran all last week. Now the local court has denied them bail.

Argentina has subsequently declared its southern port cities off limits to correspondents, not an unusual restriction in a country engaged in military operations. But the three British newspapermen were in Tierra del Fuego, and were under arrest, long before that prohibition. The government now seems to be applying its rules retroactively.

In a time of tension between two countries, it is always easy to go after the correspndents. They enjoy none of the formal and traditional protections that surround diplomats, or even soldiers. Argentina repatriated the British marines of the Falklands garrison, a decent and even courtly gesture. As the Sunday Times commented, "At least the same fairness should surely be exhibited toward peaceable journalists, doing a job which all free countries recognize as legitimate."