The commander of the British task force said it was "ready to strike" and Prime Minister Margaret Thatcher rebuffed a growing chorus of pleas from her political opposition today to delay new military action in the Falkland Islands crisis.

Rear Adm. Sandy Woodward told reporters on his command aircraft carrier HMS Hermes in the South Atlantic that the recapture yesterday of the island of South Georgia from Argentine invaders "was the appetizer. Now this is the heavy punch coming up behind.

"My battle group is properly formed and ready to strike. This is the run-up to the big match which, in my view, should be a walkover," Woodward said, voicing the bravado that has become increasingly evident since his task force began to approach the islands captured by Argentine forces nearly four weeks ago.

Neither Thatcher nor her Ministry of Defense did anything to dispel widespread speculation that British troops would soon be attacking the islands, and a Ministry of Defense blackout on "operational matters" issued at midday served to heighten the conjecture.

In a stormy, dramatic confrontation in Parliament today, reflecting the first major cracks in the previously strong public front of opposition support for the government's strategy in the conflict, Labor Party leader Michael Foot demanded that Thatcher send Foreign Secretary Francis Pym to the United Nations in response to an appeal yesterday by U.N. Secretary General Javier Perez de Cuellar for Britain and Argentina to avoid escalation of the crisis. Foot called for a moratorium on military action until such talks could be held.

With anger welling in her voice, Thatcher said, "My reply to the secretary general is to urge him to address his remarks to the junta in the Argentine."

In response, some left-wing Labor members leaped to their feet, pointed at Thatcher and screamed "warmonger" in the kind of drama that has been the hallmark of crisis debates in the House of Commons for centuries.

Foot later switched his approach, saying, "I ask the right honorable lady not to take any military action" until she held full-scale consultations with the House of Commons. An emergency six-hour debate has been scheduled for Thursday.

Echoing Foot's theme and expressing alarm at the prospect of Britain engaged in combat with thousands of Argentine troops, David Steel, leader of the small but influential Liberal Party, announced at a public meeting he would refuse to commit his party to supporting new military moves unless Thatcher agreed to confer with opposition leaders on strategy.

Thatcher, however, upheld her position, saying, "Until the terms of the U.N. Resolution are complied with, namely that Argentine forces withdraw, we shall continue to exercise our right of self-defense under Article 51" of the U.N. Charter.

Tony Benn, leader of a left-wing group in the Labor Party, charged, amid loud jeers by Thatcher's Conservative Party supporters in the chamber, that the government had always planned that "this should be a military expedition alone" and "never had the slightest intention of using the U.N. for the purposes of negotiation."

The prime minister responded in an icy tone, "The right honorable gentleman is talking nonsense."

Pym told European Community foreign ministers in Luxembourg that the mission of Secretary of State Alexander M. Haig Jr. to bring about a negotiated end to the crisis "is still very much in play" and remains the "best hope."

The Defense Ministry contributed to the sense of impending warfare with an unusual and confusing pair of statements.

Shortly before midnight yesterday a spokesman said there was "no truth" to a report in The Times of London that special Marine forces had landed on the Falklands.

Twelve hours later, the ministry clamped a blackout on all "operational matters." Another spokesman said this did not necessarily mean that the earlier denial was being repudiated.

The effect was to sow confusion and to lend credence to persistent reports that the Marines had landed an advance party on the Falklands in the same manner that they had done on South Georgia last Thursday, three days before the attack that recaptured the British island 800 miles east of the Falklands.

Col. Jonathan Alford, a leading military expert, said, however, that a full-scale assault on the Falklands, if it happens, is probably about two weeks away. If such an attack is to be carried out, he said, Britain would first have to get additional Harrier jump jets to the war front.

There are 20 Harriers aboard the two aircraft carriers in the vicinity of the Falklands but another 20 left Britain aboard a container ship only last weekend for the minimum two-week journey to the South Atlantic.

An additional 900 Marines left aboard the assault ship Intrepid today, bringing to about 5,000 the estimated number of British troops in the task force. There are now close to 70 ships in the flotilla, which is spread out across 8,000 miles of the Atlantic Ocean. So far, it is estimated that the cost to Britain of mounting the operation is about 275 million pounds (almost $500 million).

Since a frontal attack on the Falklands could be very costly in casualties, analysts expect that Britain will first attempt to attack West Falkland. It is less populated than the eastern island and probably has fewer defenders.

Argentina is believed to have up to 10,000 troops on the two islands. The hundreds of inlets breaking the coastline make it difficult to prevent the British from establishing a beachhead.

Another possibility is that small groups of highly trained commandos will carry out a spectacular raid on a fuel depot or ammunition dump or perhaps try to kidnap a leading Argentine official on the islands.