Argentina today began what is expected to be a long weekend of fervent rallying in support of its costly effort to claim the Falkland Islands as thousands gathered in front of the presidential palace to cheer for the country's territorial claims and the soldiers fighting to hold control there.

Bolstered by rosy reports of Argentine victories against the British forces surrounding the Argentine garrison at the Falklands capital of Stanley, a crowd estimated at a minimum of 10,000 gathered tonight in front of the presidential palace to celebrate the "day of affirmation of Argentine rights in the Malvinas," Argentina's name for the Falklands.

Ending a day of ceremonial events around the country, President Leopoldo Galtieri marched through the crowd to preside over the lowering of the Argentine flag in the broad, tree-lined Plaza de Mayo. The Army commander-in-chief, looking drawn and sober, stiffly saluted while the national anthem blared over loudspeakers, then turned and made his way back inside the pink stone presidential palace as the crowd cheered and chanted patriotic slogans.

The mass patriotic rally, strongly supported by the military government, came only 14 hours before Pope John Paul II is due to arrive in Argentina for a two-day visit that has become a rallying point for the country's nationalistic support for the military conflict with Britain.

Although Vatican officials have described the pope's visit as a pastoral mission to promote peace, the military government and populist civilian leaders have sought to use the event to recharge the country's morale after several weeks of military reversals on East Falkland and apparently heavy Argentine losses.

The pope's "very presence" in Argentina, Foreign Minister Nicanor Costa Mendez said today, "can mean a great uplift toward the end of aggression in the establishment of a peace which represents our rights" over the rocky, stormy islands.

The Argentine military command today continued to describe Britain's military task force in the South Atlantic as badly shaken by the Argentine Air Force's raid Tuesday on troops and ships making a landing at Fitzroy, 12 miles southwest of Stanley.

Military officials said Argentine Air Force planes today carried out strikes against British positions on Mount Kent, a strategic piece of high ground 10 miles west of Stanley. A military spokesman said the results of the attacks were still being evaluated but it appeared that the bombing had inflicted heavy casualties.

A military spokesman said in a press briefing tonight that the only other military action today was skirmishing between Argentine and British patrols near Mount Kent and Fitzroy. Spokesman Enrique DeLeon said that no "organic unit" of British troops remained at Fitzroy, although the military command believed some isolated troops may have remained there.

DeLeon repeated Argentine claims that British losses at Fitzroy had caused severe damages to the landing force and denied reports that as many as 11 Argentine planes had been shot down in the area. He said only two had been lost there. The British have imposed a news blackout on casualty figures from the raid, but unofficial press reports in Britain put the toll from the landing ship Sir Galahad at 20 dead, 80 wounded and 39 missing.

A communique issued by the military command tonight said that Argentine aircraft also launched "multiple" attacks against Fitzroy yesterday with unknown results. Late last night, the military command reported an eight-hour artillery duel between the British and Argentine lines around Stanley and claimed that Argentine fire had "neutralized the English battery."

The military command also said two British Harrier warplanes were shot down during a late night air attack on Argentine positions.

The air raids on Tuesday, which Argentina claims destroyed two troop carriers and a frigate, damaged a third troopship and resulted in heavy casualties and loss of materiel for the British, appeared to have revived public optimism here that Argentina could eventually withstand the British offensive against the estimated 7,000 troops defending Stanley.

Costa Mendez indicated to reporters today, however, that there was little hope of a diplomatic settlement that would end the British offensive and preserve Argentina's position on the islands. Asked if new developments had been made in negotiations over a peace settlement, Costa Mendez said, "I don't know of anything that you don't know about." Foreign Ministry officials said that the last attempt by U.N. Secretary General Javier Perez de Cuellar to arrange a cease-fire broke down Sunday.

The thousands who gathered in the Plaza de Mayo tonight cheered wildly as a band played patriotic marches, and loudspeakers blared exhortations such as "The chains of colonialism have been totally destroyed" and "Our men are dying so the fatherland can live."

Thousands in the crowd carried blue and white Argentine flags and the yellow and white flags for the pope. Banners, chants and signs also linked the pope to Argentina's nationalistic causes.

"The pope and Peron are a single heart," said one, referring to former president Juan Peron.

Today's holiday was created by the government to honor the day 153 years ago when Luis Bernet was appointed to be Argentina's governor of the Falklands. Four years later, Bernet and his small band of followers were expelled from the island by the British, beginning 149 years of British rule.