Argentina's joint military chiefs, in a terse communique after a day of silence, said tonight that they had ordered an air attack to prevent Britain "from reinforcing or consolidating its positions" at San Carlos on the Falkland Islands.

The communique gave no details about the attack, saying only that the "results are being evaluated."

While the ruling junta had little to say publicly about the day's military activities--and warned tonight that its silence "should not be a source of worry or strange speculation"--independent Argentine wire services continued to publish unconfirmed accounts of Army advances against the British.

One independent wire service, Noticias Argentinas, reported that Argentine attacks also "severely damaged" three British ships transporting troops and weapons.

Unconfirmed rumors circulated here this morning that the Canberra, a converted luxury liner that is one of the largest vessels in the British task force, had been hit. In what was interpreted as an indication that the Canberra is a target, the joint chiefs issued a communique this afternoon declaring that, contrary to some reports, the Canberra is not a hospital ship but is used for troop transport. The communique named four vessels that it said officially have been declared by Britain to be hospital ships: the Uganda, the Heraldo, Hecla and Hidra.

Quoting a "qualified military source," Noticias Argentinas said the Army launched a strong attack against British troops this afternoon and scored "an important advance." The area is "totally controlled by our forces" and the British are "totally isolated," the source claimed.

The land attack took place immediately after Air Force and Navy planes, taking advantage of favorable weather this afternoon, sent waves of bombing attacks beginning at 2 p.m. against British troops at San Carlos.

The bombing by Air Force Mirage jets and Navy A4 Skyhawks caused numerous British casualties, as well as damage to a troop transport, a frigate, and a ship adapted for helicopter transport, according to a military source quoted by the wire service.

At least one of the ships damaged had advanced into the Strait of San Carlos under cover of thick fog that enveloped the island during the morning and prevented air attacks, Noticias Argentinas said. The agency said the planes struck when a strong midday wind dispersed the fog.

It identified one of the damaged vessels as a logistical supply ship of the Sir Lancelot class, which would be a 5,600-ton vessel that normally carries a crew of about 68 and can carry 340 troops.

The wire service added that, according to military sources, the British troops now were "totally deprived of logistical support . . . ,which favors the advance of our troops."

The joint chiefs of staff, the only source of official information, had maintained a news blackout throughout the day. In two communiques issued tonight, the high command said that the "informational silences should not be a source of worry or strange speculation."

In an oblique reference to detailed stories out of London and unofficial reports here on the progress of the battle, the high command warned against accepting "journalistic reports . . . without official origin or confirmation." It reiterated that official communiques were the only source of reliable information, and more detailed information from the high command was expected later tonight.

Earlier in the day, President Leopoldo Galtieri sent a message to Pope John Paul II declaring that "the Argentine nation . . . is disposed to share in a cease-fire that would permit peace to be reestablished, and, in that climate, to seek a peaceful, honorable and just solution."

Justice for Argentina, however, repeatedly has been interpreted here as unconditional sovereignty over the Falklands. Galtieri showed no sign of softening on that in his reply to the pope's call for peace last week.

While official military spokesmen refused to comment on details of the fighting, a "high military source" was quoted in Noticias Argentinas saying that Argentine troops were advancing at only about 400 yards an hour on the British camp, due to the need to find new footpaths and varying approaches.

"Our actions are limited now to encircling, harassment and continuous pressure, trying to impede the advance of enemy infantry and gain whatever territory it is possible for us to gain," the source was quoted as saying.

He said, "We can't talk about results immediately, since the work of the infantrymen is very hard, entails great sacrifices, is very slow and completely anonymous."

He added that because of the rugged terrain, it was difficult for the British to receive supplies from its fleet without renewing attacks on Argentine positions. However, he said, the British fleet had withdrawn from the coast and was keeping its distance from Argentine aircraft.

The source claimed that Britain had only 500 soldiers on the tiny beach, whereas the British claim to have landed about 5,000 and claim to be gaining territory. The beach reportedly is surrounded by hills 250 yards high, impeding the advance toward the interior of the island.

Another "high military source," quoted by Noticias Argentinas, said Argentine troops had "totally stabilized the battlefront against the British disembarkation and are not allowing the British to continue their advance."

"We have good troops there who have the situation totally under control," the source was quoted as saying, adding that the Argentines "dominated the area and the bluffs that surround the English positions."

Other sources in the Air Force said that the Argentine Air Force, which had launched 72 planes in successive waves since the invasion began, continued to attack British positions at San Carlos, Noticias Argentinas reported. No details on the results of the attacks were available, however. The news agency said Canberra aircraft were dropping bombs in the area from high altitudes.

The capital, meanwhile, was quiet today. Senior military officials and soldiers' families attended a mass at the Navy chapel for Argentines who have died in the war. From the pulpit, Bishop Jose Miguel Medina, armed forces chaplain, praised the "defense of our Malvinas."

Several hundred persons crowded into an all-day sale in a magnificent 19th century mansion. It was organized by wealthy Buenos Aires housewives who donated antiques and clothes and solicited gifts from area stores for the Patriotic Fund, a government money-raising effort for the war.

As news of the battle blasted from his radio, Alberto Siles, a 61-year-old cabdriver, was overcome with emotion. "We are proud to be Argentine," he said. "I've volunteered to go. I want to fight to the death. No one will oust us from our own territory."