Argentina's military command said today its forces were still on the attack against Britian's land base on the Falkland Islands and had blocked naval operations against Argentina's own garrisons.

The military's joint chiefs of staff reported that twin-engine Canberra bombers operating from mainland air bases had attacked the British beachhead near San Carlos on the north-west end of East Falkland Island early this morning.

The command said tonight that its air attacks on British land bases hd continued during the day and the results were "in the process of evaluation."

It said British warplanes had attacked at Port Stanley, Darwin, and Port Howard across the Falkland Sound from Darwin, and that a Sea Harrier had been shot down at Darwin.

Argentine forces at Fox Bay on West Falkland Islands and at the capital of Stanley drove off attacking British warships, the military command said. It said frigates had attacked Fox Bay, and the frigate that closed on Stanley "abandoned the area at maximum velocity after receiving ground fire."

The Argentine state news agency Telam reported that Argentine and British ground forces continued to fight around San Carlos, without either side advancing. The agency said the Argentine Army was seeking to prevent British troops from taking the initiative and had "stabilized" the situation.

The government continued its show of hostility toward the United States as President Leopoldo Galtieri released his response to President Ronald Reagan's message on Argentina's national holiday Tuesday. Reagan was reported as saying "it has never been more important to reaffirm the common interests and values that unite Argentina and the United States," and Galtieri said the message "is not coherent, with the position of your government and is made incomprehensible by the present circumstances.

"If our government and people were surprised by the unexpected move of the United States to take sides with Great Britian in its conflict with Argentina, today on receiving your greeting...I couldnot be more shocked," Galtieri's note said.

The content of the two messages constrasted sharply with those published here earlier this week between Galtieri and Cuban President Fidel Castro. Galtieri said that Argentina was "deeply appreciative" of the "solidarity" of Cuba and other nonaligned nations with Argentina, and described the South Atlantic conflict as a struggle between the developing world and the West's superpowers.

Today's military account marked the first time that Argentina has reported using is aging, Brithish-made Canberra bombers in the conflict since the first air attack on the British fleet May 1. Since then, Argentina has relied heavily on its American-built A4 Skyhawks and more sophisticated French-made Mirages, but has sustained substantial losses of these planes in a week of raids on the British task force.

The Air Force commander and junta member, Gen. Basilio Lami Dozo, maintained today that "our capacity remains intact in teh south and we will continue answering whatever eventual action" by the British task force.

The afternoon newspaper La Razon said the Air Force is not suffering from a shortage of pilots and that 70 percent of the pilots shot down have been resued.

Both La Razon's and other Argentine reports predicted a major offense by the Air Force for today or Friday that would be supported by the first actions by the Argentine Navy, which until now has remained close to the Argentine coast and is believed to be hemmed in by British submarines.

Officials here indicated that Argentina might seek open justification for military support by Latin American countries during the ongoing Washington meeting of countries adhering to the Inter-American Treaty of Reciprocal Assistance, or Rio treaty.

Several clauses of the treaty provide for American nations joining together to meet an external aggression on the American continents. Argentina has not sought to invoke the military provisions of the treaty because it did not have the necessary support among the 21 member nations.

Diplomatic officials today expressed little hope that the new mediation effort by U.N. Secretary General Javier Perez de Cuellar would succeed. Last night, Argentine government representatives in the United States, including Army Gen. Hector Iglesias, told Argentine state television they had been disappointed by the U.N. resolution and believed negotiations should have been continued by the full Security Council rather than by Perez de Cuellar.

Galtieri's indication through the release of the Reagan and Castro messages of a dramatic shift in Argentina's strategic alliance was also reinforced by accounts provided to Argentine reporters traveling with the Argentine diplomatic delegation of a meeting yesterday between U.S. Ambassador Jeane Kirkpatrick and Argentine Planning Secretary Jose Miret.

Miret was reported as telling Kirkpatrick that Foreign Minister Nicanor Costa Mendez would likely head up the Argentine delegation to a meeting of the nonaligned nations group beginning in Havana this weekend. When Kirkpatrick asked for assurances that Argentina would not seek aid from the Soviet Union, according to the accounts published here today, Miret between the Soviets and the United States during World War II.