Argentine military officials said today that two military patrol boats had passed what they called a "vulnerable" British blockade around the Falkland Islands, as President Leopold Galtieri prepared for new talks with U.S. Secretary of State Alexander M. Haig Jr.

Galtieri, who was scheduled to deliver an address tonight to be broadcast by television and radio throughout Latin America, suddenly canceled the appearance and instead ordered the text of the speech distributed by his press office.

The cancellation of the address, which appealed for Latin American nations to rally behind Argentina and bitterly criticized its adversary, was seen here as an attempt by the government to moderate its tone for Haig's continued shuttle diplomacy mission.

The announcement of Haig's second trip to Buenos Aires came as Argentina's militancy appeared to be intensifying in the 12-day-old confrontation with Britain over the South Atlantic archipelago. After keeping most of its fleet far away from the 200-mile zone around the Falklands within which Britain has threatened to attack Argentine military vessels, the military here ordered two small patrol boats to pass through the zone yesterday, authorities confirmed.

The two 90-foot, lightly armed vessels, carrying crews of 16, were not challenged by British submarines patrolling the South Atlantic and Argentine authorities said today the boats had arrived in the island's principal port yesterday afternoon.

The confirmation of the boats' arrival in the islands, which Argentina calls the Malvinas, came hours after British Prime Minister Margaret Thatcher said that any challenge by Argentina to Britain's three-day-old blockade would be a "clear sign" that a search for a peaceful solution to the confrontation over the islands had been abandoned.

Britain announced the blockade by nuclear submarines after Argentina refused to withdraw an invasion force that seized the islands April 2 after 149 years of British control.

But there were no indications here today that Argentina had ordered any part of its principal navy fleet, which includes an aircraft carrier, nine destroyers and a missile bearing frigate, out of port toward the military zone.

In the text of his speech released here tonight, timed to coincide with the "Day of the Americas," Galtieri said Argentina would "remember every gesture and every word of solidarity," but added that it "could not forget the attitude of those who--perhaps looking for compensation similar to the 30 coins of Judas--deny the ideas they have put forth and defend in practice the imperialistic privilege."

Argentina, Galtieri said, had invaded the Falklands "with an absolutely limited, prudent and humanitarian use of force" after "bearing for a century and a half only silence instead of answers to our legitimate claim."

Argentina was expelled from the island by the British in 1833 and ever since has maintained that it owns the territory and that the British occupation was illegitimate. Galtieri's statement tonight stressed Argentina's argument that the islands had represented a vestige of colonialism, and said that its right to the island was "irreconcilable."

Galtieri also defended Argentina's new military political administration on the island. "Now, even under the threat of aggression on a great scale by an intercontinental power," he said, Argentina is "working to assure the best living conditions for the few residents of the territory."

Military authorities here yesterday permitted the first Argentine journalist to travel to the islands since the days immediately after the invasion.

The private news agency Noticias Argentinas reported after the trip by its correspondent that conditions on the islands were difficult as the Argentine military prepares for a possible invasion and that many residents were unhappy with the situation.

The agency reported that Argentine troops were dug in throughout the treeless terrain with heavy artillery and that C130 transport planes continued to arrive carrying further reinforcements. The governor of the island, Col. Mario Benjamin Menendez, was quoted as saying that the islands' defense force had now grown to more than 9,000 Argentine troops.

The news agency also reported that because of supply problems to the islands, rapid inflation had overtaken the islands' economy and that a Falkland pound had risen in value from 15,000 Argentine pesos to 20,000 pesos in one week.

The official Argentine news agency Telam reported, meanwhile, that seven British Marines who surrendered three days after the taking of the Falklands were being held at the military college in Comodoro Rivadavia, about 1,120 miles south of here. The agency quoted Col. Esteban Solis as saying the seven were in good health and were allowed to take part in physical fitness training with the cadets. There was no word on when the Marines would be deported.