Declaring that "what has been created here must have some claim as one of the wonders of the modern world," Queen Elizabeth II opened London's new Barbican Centre forthe Arts and Conferences on Wednesday night, one decade and nearly $300 million after she unvieled its foundation stone in 1972.

Her claim could be justified in cost, controversy and concrete alone. Over the years, a chorus of critics condemned everything from its endless cost overruns and construction delays to the cold concrete masses of the arts center and the surrounding Le Corbusier-style redevelopment area in the heart of London.

The arts center completes the fortress-like Barbican project, named for its location on the site of Roman and medieval fortifications in the semi-autonomous, mile-square financial district known as the City of London. Where, on Dec. 29, 1940, German bombers leveled 70 acres of narrow streets and old buildings, London's tallest apartment buildings now tower over excavated remnants of Roman wall and the rebuilt medieval Church of St. Giles, the only survivors of the bombing. These now stand amid reflecting pools, lawns and gardens on a raised, windswept pedestrian plaza of urban planners' dreams.

An afterthought in the original Barbican plan, the arts center has emerged from years of argument as the largest project of its kind in Europe. Seen here as a rival to the Lincoln Center in New YorkSee BARBICAN, G2, Col. 1 From AP The Barbican's concert hall. London's ---New Palace ---Of the Arts ---BARBICAN, From G1 and Washington's Kennedy Center, the 10-story structure contains a concert hall for the London Symphony Orchestra, two theaters for the Royal Shakespeare Company, a new home for the Guildhall School of Music and Drama, a central library for the City of London, an art gallery, a sculpture court, three cinemas, two restaurants, a pub, and numerous bars in hidden corners of its intricate, dramatic interior.

To help pay for what the lord mayor of London, Sir Christopher Leaver, told the queen was the City's "gift to the nation," financed entirely by Corporation of London taxpayers, there also are facilities for international conferences, already booked well into the mid-1980s.

The Royal Shakespeare Company says advance reservations for the coming season at the Barbican are 40 per cent higher than the same period last year in a smaller, old theater it occupied in London's West End, and the London Symphony is selling American-style season subscriptions. The center is expected to break even on operating expenses in five years, but the Corporation of London is unlikely to recover the cost of construction, just as critics had warned.

But worries that patrons would find the brave-new-world architecture of the center too impersonal--if they find it at all through the maze of City streets seldom used at night and the Barbican's own forbidding concrete access roads beneath the elevated pedestrian deck--appeared to be dispelled by Wednesday night's nationally televised, black-tie royal opening.

More than 3,000 invited dignitaries, celebrities and journalists-- including such familiar faces as Laurence Olivier, Joan Plowright, Douglas Fairbanks Jr., Harold Pinter, Jeremy Irons, Judi Dench and former prime minister Sir Harold Wilson--joined the queen for the opening ceremony heralded by the royal trumpeteers, performances by the London Symphony and the Royal Shakespeare Company, a peek at the art gallery's major opening show of postwar French paintings, a fireworks display on the outdoor terrace and a buffet champagne supper.

Entertained by horn and wind ensembles, guests in tuxedos and fancy gowns picnicked throughout the varied plush-carpeted open spaces on the center's many levels, joined together by open staircases and balconies. Well before the champagne stopped flowing, critics were grudgingly admitting they liked much of what they saw and heard. It turned out, one said, that a building promising little from the outside had been ingeniously designed on the inside.

"Obviously the place is going to work and work well," award-winning architect Roderick Gradidge wrote in The Times. Despite his antipathy to the Barbican as "the last in a long series of palaces of culture built in London which are entirely dedicated to the concrete brut ideals of Le Corbusier and his brutalist followers," Gradidge was impressed by "the masterly planning . . . on the simple functional level" and how the concrete mass had been softened by the liberal use of natural wood, bold colors, and sumptuous fittings.

The man from The Sunday Observer said, "Of all the arts centers I know, the Barbican is the least like an airport terminal."

After Wednesday night's London Symphony concert featuring conductor Claudio Abbado, pianist Vladimir Ashkenazy and cellist Yo Yo Ma, the imposing, 2,026-seat concert hall also drew praise for its natural wood paneling and acoustics, fine-tuned by clear plastic balls hung from the ceiling. The London Symphony, concluded the music critic of The Financial Times, "has at last a concert hall worthy of an orchestra bearing the city's name."

The new London home of the Royal Shakespeare Company in the dramatic, brown-toned, 1,160-seat main theater of the Barbican was judged by the same newspaper's architecture critic "one of the most interesting new theaters in Europe." Like the concert hall, the theater is unusually wide with shallow balconies, putting the most distant seat only 65 feet from the focal point of the stage. Its fly tower is an outsized 109-feet high to accommodate scenery and effects rotated here from the company's Stratford-on-Avon theater.

The development of the Barbican Center has been shepherded through against formidable difficulties by Canadian-born Henry Wrong, who earlier had helped move the Metropolitan Opera to the Lincoln Center in New York and develop the Canadian National Arts Centre in Ottawa. He became the Barbican Centre's administrator in 1970, shortly before the Corporation of London's council voted by a narrow majority to begin construction after decades of wrangling over concept and cost.

Wrong acknowledges that the Barbican Centre will be competing for customers with the nearby South Bank cultural complex on the Thames, which includes the Royal Festival concert halls, the National Theater, the National Film Theater and the Hayward Art Gallery--a total of eight auditoriums, and a large gallery.

Although Wrong expects the Barbican to draw new patronage from among City businessmen and outsiders attending Barbican conferences, some gains may have to be made at the expense of the South Bank.

But The Times urged a longer view in an editorial comparing the postwar construction of these cultural centers with the great Victorian programs of the 19th century that produced the Albert Hall, the Royal Opera House Covent Garden, many London theaters and most of its best-known museums. The Barbican Centre alone, enthused The Times, "is a piece of public munificence of a character nothing less than noble."