'Mission impossible' at the UN

Mission impossible.

This is how some United Nations officials describe the mandate handed by the Security Council to UN Secretary-General Javier Perez de Cuellar.

The resolution asks him to get Britain and Argentina to agree to a cease-fire within seven days and to renew his efforts to bring about a peaceful solution to the Falklands crisis. But it contains only the vaguest reference to Resolution 502 adopted by the council on April 3, which calls for an immediate cessation of hostilities, withdrawal of all Argentine forces from the islands, and a diplomatic solution to the dispute.

Observers here say that as a result of the radically altered military situation, it is unlikely that Britain will agree to either withdraw its troops from the islands after it has recaptured them or to a cease-fire before it completes repossession.

''Argentina at this point is left with no choice at the bargaining table but to sign its surrender. It may be better off if it refused to negotiate and claimed to have lost the battle but not the war,'' says one Latin American diplomat.

In the long run, observers say, the price for holding on to the island might prove to be too high for Britain. Argentina could then hope to renegotiate from a stronger position.

The Secretary-General considers his task to be ''very difficult indeed.'' If he pushes too hard at this point, he might anger the British. If he does not move forcefully enough, the Argentinians might accuse him of being too passive.

''He moves on a tightrope. One simply cannot see him getting Britain to renounce at the bargaining table positions that it has secured through military means'' says one analyst.