Britain has landed more than 3,000 additional troops on East Falkland Island in preparation for a final assault on the Argentine military garrison at Stanley, according to a dispatch filed today by a British journalist in the war zone.

The report, which apparently slipped through British military censorship and was ordered suppressed within an hour after release, followed another dispatch in which Britain's ground force commander told reporters that his attack plans were proceeding on schedule. But as of tonight it was unclear whether fighting for the Falklands capital had begun.

In Buenos Aires, the military high command reported artillery fire around Stanley and said both sides sent out patrol missions. In a late communique, the joint chiefs added that the British lines remained static today with very reduced activity," Washington Post correspondent Margot Hornblower reported. Sources said the Argentine forces had been resupplied by air from the mainland and were prepared to resist a final British assault.

Meanwhile, a conference of nonaligned nations in Havana gave preliminary approval yesterday to a resolution "deploring" British military action in the South Atlantic and demanding an immediate end of U.S. support for Britain. Argentina hailed the statement as a "victory" although the resolution's language was toned down before passage.

The report of the troop landing, filed by Jeremy Hands, correspondent for Britain's Independent Television News, said the forces had landed at an undisclosed location, "consolidated ashore and are moving rapidly into positions close to Stanley."

But before the story could be broadcast, the British Defense Ministry put out a request to editors that the information be suppressed. The request went out 45 minutes after the dispatch ran on the wire of the Press Association, Britain's domestic news agency.

The Defense Ministry, which maintained a news blackout on ground fighting for the fifth straight day, has consistently refused to disclose the whereabouts of the reinforcements, despite unconfirmed reports in London that they had landed on the islands. The apparent slip-up in censorship provided the first independent confirmation of the landing from a reporter in the war theater who would be able to see the troops.

The reinforcements, shipped to the South Atlantic aboard the requisitioned cruise liner Queen Elizabeth 2, bring Britain's troop strength on the island to at least 8,000, probably at least a match for Argentina's Stanley garrison.

At a news briefing at Darwin, an East Falkland settlement that British troops seized a week ago, the British ground forces commander, Maj. Gen. Jeremy Moore of the Royal Marines, told reporters that Argentine forces have been "squeezed into a little corner around Port Stanley." While he refused to say when his forces would assault the garrison, Moore said, "I am tremendously pleased with the way everything is going. We are not behind in our schedule."

"I will not discuss my timetable for Port Stanley," Moore said. Referring to his Argentine foe, he added: "Keep him guessing. That's good for him."

The pooled report of the briefing, written by Richard Savill of the Press Association, was also censored. The Press Association was unable to say when the briefing occurred or when the dispatch was written.

The Argentines "will be a little more squeezed before we are finished," Moore said, but added, "I don't want us dashing in there, causing unnecessary loss of life of my soldiers. We will do it the attack in a proper, sensible, well-balanced, military way."

While Moore said British forces had encountered little resistance and only occasional shelling from the Argentines, he did not rule out the possibility of an Argentine counterattack, either from Stanley or the mainland.

Referring to the Argentine foe, Moore said, "If he tries to come out and have a go at my troops, he is welcome."

The only information provided by the Defense Ministry today involved the transfer of wounded Argentine prisoners to an Argentine hospital ship and the arrival in Britain of captured Argentine naval officer Alfredo Astiz.

Astiz is being held at a military barracks. He is wanted for questioning by French and Swedish authorities about the alleged torture and deaths of three women in Argentina several years ago.

Correspondent Hornblower added from Buenos Aires:

The Argentine press was filled with reports today, citing unofficial military sources, that about 2,000 Argentine troops are prepared to mount a counteroffensive against British beachheads at Darwin, San Carlos and Goose Green, on the western side of East Falkland. Sources said 1,500 soldiers have already taken up positions, presumably reinforced by Argentine garrisons on West Falkland Island.

Meanwhile, about 9,000 Argentine troops--30 to 40 percent of them professional soldiers--have formed a "horseshoe of combatants" ready to defend the Falklands capital without hesitation, military sources said.

Despite British reports that Argentina has lost up to a third of its planes, Air Force Commander Basilio Lami Dozo said that air power is "practically intact" and that the Air Force and the Navy air command had received equipment and ammunition from friendly countries.