The U.N. Security Council adopted a resolution today calling on the secretary general to negotiate "mutually acceptable terms for a cease-fire" in the Falklands and asking him to report back within seven days.

Although the resolution was adopted unanimously, and Britain and Argentina announced their willingness to relaunch the talks, there was no expectation that this would have the slightest impact on the fighting.

Britain successfully opposed any resolution calling for an immediate cease-fire, and after six days of debate the council reluctantly went along.

"The fact that they are negotiating does not stop the fighting," Secretary General Javier Perez de Cuellar told reporters. "That is in a way the rule of the game. I will do my best, but it will be a very difficult mission indeed."

The negotiators -- Sir Anthony Parsons for Britain and Arnoldo Listre for Argentina -- made separate visits to the secretary general's office later this afternoon. This was a resumption of the familiar pattern of mediation that had gone on for two weeks only to end in stalemate last Friday, just before the British landing on the islands.

Yet, the situation Perez de Cuellar faced today was different, with the fighting far more intense and the parties wider apart on settlement terms than they were when he stopped.

Parsons said the secretary general had asked a number of questions of Britain -- for which, Parsons said, he would have to refer to London for answers -- rather than setting out his own ideas on how to proceed.

Perez de Cuellar expressed his frustration at the time limit, asking, "What can I do in seven days?" He chided the Security Council by saying that "the terms of reference may not provide a sufficiently clear and precise guidance either to the parties or to myself."

The secretary general and Argentina had wanted the resolution to set, as the "basis" for the talks, the resolution adopted by the council on April 3 that called for an end to hostilities, Argentine withdrawal, and negotiations, plus the proposals made by Perez de Cuellar in his first mediation effort: a cease-fire, mutual troop withdrawals, an interim U.N. administration of the islands and negotiations to resolve the sovereignty issue.

Britain rejected such rigid ground rules, however, and the resolution adopted simply asks the secretary general -- not the parties -- to "bear in mind" the April 3 resolution and Perez de Cuellar's own earlier proposals.

After the vote today, Parsons outlined to the council the stiff British conditions for a cease-fire, saying it "should be unequivocally linked with an immediate commencement of Argentine withdrawal" from the islands.

A simple verbal agreement by Argentina to withdraw will not suffice, he said, adding that there must be "practical and irrevocable arrangements for an Argentine withdrawal."

Parsons also noted that "the situation has changed" since Britain accepted the provision for mutual withdrawal in the Perez de Cuellar peace plan. "We cannot now accept that Argentine withdrawal be linked in any way to a parallel British withdrawal," he said.

Listre, speaking for Argentina, told the council that "we go to the negotiations without preconditions" and "without giving up any of our rights."

Many diplomats here gave today's round to the British. They noted that Argentina could not win sufficient Third World support to force a British veto.

The resolution adopted today was based on an Irish draft that initially included a 72-hour truce, but Britain had vowed to veto this. The search for common ground was undertaken yesterday by Ambassador Olara Otunnu of Uganda, who carved out language acceptable to Britain, Argentina and the secretary general.

Otunnu won his reputation as a problem-solver last year when he devised a formula to break the election deadlock between Kurt Waldheim of Austria and Salim A. Salim of Tanzania, with the result that Perez de Cuellar became the secretary general.