For the third straight day the Defense Ministry today maintained a blackout on information about ground fighting in the Falkland Islands amid expectations that British troops would launch an assault shortly on the main Argentine garrison at Stanley, the capital.

Officials from Prime Minister Margaret Thatcher down insisted that the pause since the capture of ridges commanding the western entrance to Stanley early this week was strictly for military reasons, to get troops and supplies to the front, and not for diplomatic purposes. There is no optimism here that Argentina will agree at the last hour to withdraw peacefully.

Argentina's military command had little to report on the situation in the islands and both the government and the country seemed to be simply waiting for the decisive battle to begin, Washington Post correspondent Jackson Diehl reported from Buenos Aires.

Argentine officials reiterated their intention to fight for the islands rather than accept Britain's demands for an unconditional withdrawal and said there was almost no hope of a settlement that would prevent the fighting.

The pattern in the two-month-old Falklands conflict has been that news blackouts and military pauses have preceded major action by the British task force.

For the last three days, the only news of fighting has come from delayed, censored dispatches from correspondents with the task force. At times the reports have contained information several days old. Tonight Independent Television News reporter Jeremy Hands reported from a position overlooking Stanley that the British were prepared for the assault and there appeared to be little standing in the way of their entering the town.

British Harrier jets have dropped thousands of leaflets on Stanley urging the Argentine forces to surrender, according to reports from the front.

One set of leaflets includes a "safe conduct" pass in English and Spanish on one side. On the reverse is a letter from Rear Adm. Sandy Woodward, commander of the British task force, to his Argentine counterpart, Brig. Mario Benjamin Menendez, who has reportedly ordered his men to fight to the last.

Woodward's message says: "The forces under my command have established a dominating presence in this area and there can be no prospect of your garrison being relieved. Matters have now reached the point where you must consider whether there is any further point in maintaining resistance in the face of such overwhelming odds."

A second leaflet cites the example of the surrender of Argentine forces on South Georgia on April 24 and reproduces a photograph of Lt. Commander Alfredo Astiz signing the surrender document.

"We do not wish to spill more blood but if there is no alternative, we are prepared to do so," the leaflet says. "More useless deaths will only create more disconsolate mothers."

A senior Defense Ministry source said, however, that "I think there has still got to be some kind of fight. I think we'd be extraordinarily fortunate if they gave up before the end of next week."

If the surrounded Argentines choose to fight for every bit of territory, analysts predict hundreds would be killed.

The fierce battle for Goose Green, 50 miles west of Stanley, last weekend demonstrated the high rate of casualties. About 1,600 Argentine troops were involved in the fighting and 250 were killed and 140 wounded, an unusual death-to-injury ratio.

Maj. Gen. Jeremy Moore, the Marine commander of British land forces, faces a 7,000-man Argentine garrison at Stanley.

One key question is the effectiveness of Argentina's Air Force, which is believed to have lost more than a third of its operational planes and many pilots last week during mass air raids.

The Argentines are well dug in along a continuous, curved line from the southeast to the northeast, and there are no flanks to turn. Moore may thus have to resort to a frontal attack, although that would probably be the last resort and the most costly for both sides, military analysts said.

With the British having the advantage of mobility through the use of helicopters, Moore is likely to try to surprise the Argentines, perhaps through a paratroop assault or by establishing a new beachhead near Port Stanley, according to analysts.

Officials of Cunard Lines, which owns the QE2, told relatives of crew personnel that the ship is not in the "danger" zone. They announced today, however, that Cunard will not get the requisitioned luxury liner back until at least mid-August.

Diehl added from Buenos Aires:

The Argentine military command reported tonight that military action on the Falklands today had been limited to exchanges of artillery fire. A military communique said Argentine artillery fire had been concentrated on the area of Mount Kent, where British forces have established positions overlooking the approaches to Stanley.

At Buenos Aires' port, a crowd gathered to greet the returning crew of the fishing boat Narwal, sunk by British war planes in the blockade zone near the Falklands last month.

The Argentine military command claimed at the time of the attack that British planes had bombed the boat, then ruthlessly strafed survivors as they attempted to escape in life rafts, while ignoring calls for assistance.

But the several dozen crew members of the ship arriving today said they had been picked up by British helicopters after abandoning their boat, and added they had been treated well by the British before being released.