It has been a confusing, heady week for the British. They have watched the fleet steam off threatening to do battle over a group of wind-swept islands off the coast of Argentina, with one popular newspaper publishing a "war special" and another declaring, "One Week to Win" across the front page.

But at the Allsop Arms, one of many pubs where Londoners go to discuss their problems and politics, there is no shortage of opinion.

"The Falkland Islands?" mused Charlie Ponsonby. "To tell the truth I didn't even know they existed until a week ago, and then I thought they were somewhere just off the coast of Scotland. But now that I know what it's all about, I think we should definitely give the Argies a good kick up the backside." And as Charlie raised his pint of ale in the Allsop Arms, the pub was with him to a man.

"Did you see our fleet going off?" asked one young man sporting a punk hairdo and an earring. "Well it's something to get roused up about isn't it? This country has been down for so long--it's about time we had something to stand up for."

The Allsop Arms is one of those tiny London pubs where your head almost collides with the roof beams. Lunch time conversation among the half a dozen or so regulars usually runs to the latest woes of the local football team and what the government's economic policies have done to the price of ale. This week national pride is at stake.

"There's only one thing for it, we've got to go in there and get them out," said Ruby Hockney of North London, talking about the Argentine invaders.

Bartender John Beale sounded a note of moderation. "Everyone is talking about standing firm on this. But to me it sounds like the 19th century. These aren't the days of Adm. Nelson, as a lot of people seem to think."

At these conciliatory words, a voice boomed from a corner of the bar. "This is the first time I've opened my mouth in three months but I'm opening it now," said Stewart Nichol. "This is a make-or-break situation. I came 3,000 miles from Canada to fight Mr. Hitler, and I'd go as far again for Britain. Let's face it. We can't give in. Either Thatcher goes or it's off with Argentine President Leopoldo Galtieri's head."

No one doubted the iron determination of Margaret Thatcher, the British prime minister, to regain the Falklands, but there was a lot of talk, and some mystification, about America's role as conciliator. "It beats me what it's got to do with America," said Ruby Hockney. "I think Reagan should keep his nose out of it."

Bartender Beale disagreed. "This American bloke, what's his name, Haig, I think he's doing a good job. He knows that it's all about losing as little face as possible."

The patriotic fervor here and elsewhere in Britain has been widely echoed in the press.

While serious newspapers like the London Times, the Guardian and the Daily Telegraph have published long analyses of the politico-military situation, the popular press has been far less restrained.

The popular tabloid The Sun proudly published the words of a song which it said helicopter crewmen in Britain's armada sailing to the Falklands were singing. Part of the song, based on "Don't Cry for Me, Argentina," from the musical "Evita," goes like this: "Get on your bike, Argentina . . . , you've gone too far now, we've left the bar now, and soon the Falklands will be in our hands."

A great deal has been made of the fact that Prince Andrew, Queen Elizabeth's second son, is serving as a sublieutenant and copilot aboard a helicopter on the aircraft carrier Invincible, now Falklands-bound.

There is some tough talk aboard the Invincible. When a sidewinder missile was test-fired near the carrier, the news of the world quoted a pilot as saying "that would make an Argie's eyes water if it hit him up the rear."

But the lighthearted talk and bravado concealed serious concern widely felt for the crews of the ships in the flotilla, on an adventure virtually into the unknown about 7,000 miles away from British shores.

So far, the British have kept their cool in public and there have been virtually no anti-Argentine demonstrations. But two hotel porters, David and Andrew Banks, did let their feelings get the better of them when, garbed in Union Jacks, they hurled cans of Argentine corned beef through windows of the Argentine Embassy.

After being fined 50 pounds in a London court, David Banks said, "We'd do it again."