PORTERS WITH their traditional blue-trimmed hats, back at their normal dock-side posts, greeted tourists and pleasure-seekers arriving by train from Belgium's Waterloo station. Eighteen hundred passengers, loaded down with trunks, suitcases and all the paraphernalia of transatlantic travel, stroke up the gangplanks to the 13-story cruise ship, smiling briefly at the main door as the ship's photographer snapped their picture.

The Queen Elizabeth II, England's most-celebrated participant in the Falkland Islands war, was resuming her civilian duties, setting sail Aug. 14 from Southampton on England's southern shore for New York, scarcely showing a battle scar.

Inside the vessel, passengers found the requisite appointments of luxury travel, some old and some new: fine china and crystal in the ship's dining rooms and seven grand pianos stationed in elegant ballrooms. Plus: jacuzzi whirlpools, ballet barre and mirrors in the ship's new health facility (called the California Golden Spa), and the new Parcours jogging and exercise course on the main deck. Soon the ship will have a glass-covered lido on one deck, allowing passengers to use the outdoor pools during all seasons. Additionally, the QE 2's exterior was repainted in white and pebble gray instead of the pre-war biack and white, one of a number of decorative changes made during the 60-day, $10-million remodeling. The alterations also include a completely redecorated night club, which was gutted and redesigned, making room for a buffet area that stretches onto the deck.

Even the menu has changed. Health food has been added to the daily bounty and plans call for an outdoor health-food bar.

Cunard officials, bubbling with enthusiasm over the Queen's return to Tourist duties, have announced a series of new on-board activities, including a wider variety of lectures, seminars and exercise classes. They also promise special excursions and travel fares on many of the Queen's 1982 and 1983 cruises.

Beyond the visible changes apparent to those aboard the inaugural trip, other embellishments were hidden. Twenty thousand bottles of wine rested in the ship's cellar. In the kitchen, 150 pounds of caviar had been stored away for the passengers. And for their pets, there was the air-conditioned kennel.

Two months earlier, the Soldier Queen had displayed an entirely different personality -- the grim determination of war -- as she returned to British waters after her risky 30-day military tour in the South Atlantic, carrying home grenades, helicopters and 3,000 troops from Britain's celebrated Fifth Regiment.

As a warship, her roster had listed not the customary international passengers but young seamen who had come strictly from places such as Bristol and Liverpool and Sheffield and Manchester, many of whom never had dreamed of sailing on one of the world's greatest luxury liners. They bunked on military cots in the ship's main casino (the gambling tables had been removed), bought cigarettes and toiletries in a makeshift "PX" and consumed 432,000 cans of beer and 3 million candy bars.

To prepare the ship for military duty, two of her four swimming pools had been filled with 300 tons of steel so helicopters could land. Carpeting, 17 miles of it, had been removed or covered with protective fiberboard. Many of the ship's furnishings, including the china and crystal, had been stored in warehouses on the mainland.

Now with the ship's temporary duty over, the troops disembarked, their munitions were unloaded, the swimming pools were refilled with water, carpets unrolled, china unpacked and the Queen restored to all her peacetime glamour, once again presenting the glittering smile of pleasure.

Until the Falklands crisis, the 67,107-ton flagship of the Cunard Line had sailed only in peaceful waters since her maiden voyage in 1969, transporting passengers roughly a dozen times each year between Great Britain and North America and circling the globe for her annual 90-day world cruise. Travelers pay between $1,095 to $5,725 to sail across the Anlantic and up to $250,000 for penthouse suites on the world cruise to such exotic ports-of-call as Barbados, Rio de Janeiro, Cape Town, Honolulu, Hong Kong and Acapulco.

Luxury-class sailors are treated to all the amenities -- Rack of Lamb Bouquetie reand Tournedos Saute' Chasseur; QE 2-label scotch whisky, blend or malt, for $42 per flagon -- as well as glimpses of celebrities who, over the years, have included Yoko Ono, Linda Ronstadt, Tennessee Williams, Elizabeth Taylor and J. Paul Getty. For tourist passengers, the experience is somewhat less luxurious: small cabins and assigned seats at meals.

The QE 2 has a distinguished ancestry, dating back to the 1,154-ton paddle-wheel steamer Brittania, the first ship to make regular transatlantic crossings. Conceived by a Nova Scotia merchant, Samuel Cunard, and financed by English and Scottish businessmen, the Brittania first sailed from Liverpool in 1840. Her passage took 14 days at a speed of roughly 8.5 knots. She carried cows on board to provide fresh milk, which was served only to women and children. Like her modern-day descendant, she booked many celebrities, including Charles Dickens.

It was Cunard's reputation for speed -- which company officials have tried to play down over the years to avoid giving the impression that speed is a higher priority than safety -- and comfortable travel that accounted for much of the line's success over the succeeding years. And it was speed that made the QE 2 an ideal troop carrier for the Falklands crisis. She is, after all, the fastest passenger ship in the world (and the only one that still makes regular transatlantic crossings).

After the British government detailed the QE 2 to Falklands duty in May, it took only 10 days to fashion her into a war vessel. About 640 of the 1,040-person crew volunteered to serve during the Queen's military assignment, including the captain, Peter Jackson, who agreed to sail her to the frigid South Atlantic. Enroute, the QE 2 traveled at 26 knots without an armed escort, and once she reached the war zone she operated without any lights or radar to avoid detection by Argentine submarines. "We were aware that the Argentines were looking for us," says Jackson. "This ship was a prime target. If they could have found us it would have changed the war. It would have been a big boost for their morale."

Only once, while his ship picked her way through 100 icebergs, did the captain turn on radar. Weather conditions, including dense fog, "protected us," says Jackson, who was aided by a naval tactician and in constant touch with London. And, he says, "We changed our plans daily.

"We were spotted twice by Russian intelligence-gathering vessels. But we kept far enough out of view of reconnaissance planes. We were in danger without any doubt."

Before the end of the year, the Queen will make 11 transatlantic crossings and several cruises ranging from two to 19 days. "She is the ship that went to war," said her captain proudly as his vessel completed her facelift. "We're going to come back out and show her off in a big way."