Britian celebrated the eve of the marriage of Prince Charles and Lady Diana Spencer tonight with a music and fireworks extravaganza and the lighting of a chain of traditional bonfire beacons that reached through the night to every corner of the island kingdom.

The center of the capital turned into a giant block party as hundreds of thousands of people packed its streets and royal parks. Several hundred thousand joined the royal family and foreign dignitaries in Hyde Park for Britain's biggest pyrotechnic spectacular ever, and Prince Charles lit the first in the chain of more than 100 beacons linking London with the Channel Islands off the French coast to the south, the Scilly Isles off Land's End in Cornwall and Caernarvon Castle in Wales to the west, and the Hebrides islands of Scotland and the Orkney and Shetland islands to the north.

Multitudes more cramped out along the procession route from Buckingham Palace to St. Paul's Cathedral in a sea of red, white and blue Union Jack flags, buting, hats, T-shirts, and cushions to wait for Wednesday morning's royal wedding pageantry. The air was electric with excitement, and with an abundance of street entertainers and vendors hawking their wares, the scene resembled the medieval fairs attracted by past royal tournaments.

Much of the rest of the country watched the festivities and a rare interview of Charles and Diana on television. After the wedding there will be traditional street parties and civic celebrations throughout the nation.

In contrast to good-natured commotion over the wedding, there were remainders today of the violence that has recently beset English cities and British-ruled Northern Ireland. While gangs of black and white youths battled police in Liverpool's Toxteth district for the third consecutive night, security forces in Ulster survived two ambush attempts by Irish nationalist gunmen in Belfast without injury and defused a 400-pound remote control bomb in a trailer on a rural road near the Irish border.

In an unconnected incident, Buckingham palace officials and police in Gloucestershire west of London confirmed that two palace footmen were arrested nearly two weeks ago in connection with the theft of gelignie, explosives and detonators from a coal mining site. Officials denied a tabloid newspaper report that the explosives were found in Buckingham Palace. They said the crime was not terroist-related, but provided no other details.

Diana spent her last night before becoming princess of Wales at Clarence House, near Buckinham Palace, with Charles' grandmother, Queen Mother Elizabeth, her own mother, Mrs. Frances Shand-Kydd, and her grandmother, Lady Fermoy, who is the queen mother's lady-in-waiting at Clarence House. In the royal couple's television interview, Diana said, "I'm going to be tucked up in bed I think, early at night."

Prince Charles said in the interview that he couldn't wait for the wedding ceremony in St. Paul's, much of which he and Diana helped plan. "I want everyone to come out," he said, "having had a marvelous musical and emotional experience."

Though laughing when he said it, Charles added, "I shall, I think, spend half the time in tears" because of the music he has chosen and the way he expected it to be performed in Christopher Wren's massive cathedral.

"I've always longed to have a musical wedding," the prince said. "One of the reasons I particularly wanted to be married in St. Paul's is because I think that, musically speaking, it is such a magnificent setting."

In addition to Elgar's "Pomp and Circumstance" and other stirring music by British composers, Charles said he chose the hymn "Christ Has Made the Sure Foundation" because of its "most marvelouse melody." Diana said she chose "I Vow to Thee My Country," which "has always been my favorite since school days."

Archbishop of Canterbury Robert Runcie, who will conduct the service, has said he hoped the wedding would help unify the troubled British nation and that it would be "a sort of family gathering" that will enable Charles and Diana "to know as they pledge themselves to each other before the alter of God that they were surrounded and supported by millions of friends."

It should certainly seem that way, as people have come from all over the country for the wedding, despite its all-day coverage on television. The crowds filled the western half of Hyde Park tonight around the fireworks palace, which resembled one used for a similar celebration in nearby Green Park in 1749 at the end of the War of Austrian Succession.

Hundreds of boy scouts with flaming torches lined a route through the crowds and sultry darkness for Nancy Reagan and nearly 150 other visiting dignitaries, including monarchs, heads of state, and prime ministers. The guests were driven in buses from a Buckingham Palace dinner to sit with the royal family in a celebrity stand, which stood opposite a palace fecade built like a movie set on scaffolding in the middle of the park.

Like the supporting cast of an epic film, European kings and queens, Prince Rainer and Princess Grace of Monaco, French President Francois Mitterrand, Canadian Prime Minister Pierre Elliott Trudeau, the crown prince and princess of Japan, the King and queen of Tonga, and the presidents, prime ministers and governor-generals of the former British empire stepped out of the buses and walked to the stand, bathed in bright television lights.

Queen Elizabeth II, Prince Philip and their children, Princes Charles, Andrew and Edward, and Princess Anne followed to roaring cheers.

Charles then lit the bright torch in the middle of the fenced-off ground in front of the fireworks palace and signalled -- with the help of electronic relays from the top of the Post Office tower in London -- the lighting of the other beacons across the country, most of which were bonfires 20 to 30 feet tall.

The dignitaries and much of the crowd in Hyde Park were able to watch on a giant television screen as the bonfires were lit at Althorp, the eastern England estate of Lady Diana's father, Lord Spencer, and at Caernarvon Castle in western Wales, where Charles was formally invested as Prince of Wales by his mother, Queen Elizabeth II, in 1969.

In coordination with the "Music for Royal Fireworks," written by Handel for the 1749 fireworks show, special explosive effects illuminated the family and school crets, badges of regiments, and knighthood honors associated with the prince of Wales on the facade of the fireworks palace, while rockets exploded overhead and cannons fired on the ground. The 20-minute show, which consumed 2 1/2 tons of fireworks, ended with spectacular aerial explosions and the rising of a giant, revolving sun to 170 feet above the ground, shooting out sparkling flares.

Many in the crowd moved during the night to the two-mile wedding procession route -- from the Mall to Trafalgar Square, the Strand, Fleet Street, Ludgate Hill and finally St. Paul's -- to wait for the 11 gold-encrusted royal carriages, 200 mounted troops of the Household Guards in glittering breastplates and plumed helmets, and polished black Rolls Royce sedans taking the European monarchs, the royal family, the groom and the bride to the ceremony.

Corrdinating everything behind the scenes are the Queen's Lord Chamberlain, Lord Maclean of Duart and Morven, 64, chief of the Maclean clan, who is in charge of the proceedings; Col. Sir John Miller, 62, the crown equerry and master of the royal mews, who supervises the queen's horses, carriages and cars; and Maj. Gen. Desmond Langley, 51, commanding general of the London district of the British Army, who directs the nearly 3,000 men from Britain's armed forces and Commonwealth armies lining the procession route.

The wedding has been called the biggest media event ever, with 21 television cameras inside the cathedral alone broadcasting the ceremony to an estimated 750 million viewers in 50 countries. A giant British Broadcasting Corp. television studio has been divided into broadcasting booths with monitors for commentators to describe the scenes on the screen into 34 foreign languages.

"It's become a world event," the Dean of St. Paul's, the Very Rev. Alan Webster, said today. "There is now a real international sense that we all want it to work."