A U2 concert, by definition, should be a musically inspiring and emotionally overwhelming experience.

Intensity, passion and glorious exhaustion form the essence of U2 live, as captured on film and on record with the 1988 release of Rattle and Hum.

Unfortunately, the musical direction and live performance style of this Irish super-group has dramatically changed in the four years since Rattle and Hum, and the band's Zoo TV production March 13 at the Worcester Centrum had neither the look or feel of a U2 concert.

Opening with eight songs from Achtung Baby and virtually ignoring their existence before The Joshua Tree ("Pride (In the Name of Love)" was the notable exception), U2 intentionally divorced themselves from their past and thus alienated and disappointed many in the crowd who prefer the simple passion of U2 past to the bizarre high-tech production of U2 present.

Even when U2 deigned to give the crowd such beloved relics as "With or Without You" and "Running to Stand Still," the hollowness of their performance and the almost begrudging acknowledgement of their history weighed heavy in the darkness surrounding Bono's spotlight.

Live performance is the true test of the strength of a band's material, and the Zoo TV concert illuminated all the subtle differences between Achtung Baby and its more worthy predecessors.

Though seclusion in a Berlin studio enabled U2 to produce the industrial grunge and searing riffs of "The Fly," the innovative blend of a wicked guitar groove with vocals ranging from gospel heights to darkly sexual depths could not be effectively reproduced in concert.

Even the best and most popular tracks from Achtung Baby, such as "One" and "Mysterious Ways," suffered in live performance. Over-familiarity from excessive radio airplay combined with the band's unremarkable and unenthusiastic presentation to make fine material almost boring.

The inclusion of the new album's less impressive material, such as the virtually pointless "Who's Gonna Ride Your Wild Horses?", seemed unnecessary and frustrating when many of the best U2 songs were left off the set list. The most disappointing and inexcusable omission was the band's failure to perform such classics as "Sunday Bloody Sunday," "New Year's Day," and "Exit".

The band performance and crowd response noticeably improved when U2 finally began to play material from past albums. Walking along a narrow platform to a small stage on one side of the floor, the four members of U2 performed an acoustical version of "Angel of Harlem" with spirited vocal accompaniment from virtually every member of the audience.

The emotional impact of U2's performance steadily increased with each selection from U2's earlier albums, reaching a climax for both band and crowd with "Pride (In the Name of Love)" the only track performed from The Unforgettable Fire.

Numerous video and television screens placed about the stage showed black and white footage of a speech from the Rev. Martin Luther King Jr. about whom some of the powerful lyrics of "Pride" had been written. The music and lights gradually faded until King's speech dominated the dark silence of the arena.

U2 made effective use of their video technology throughout the show, especially during several tracks from The Joshua Tree. Rather than simply showing close-ups of the band members and action onstage, the video presentation coordinated film clips, powerful phrases and strong visual imagery with the set list, thereby giving an added dimension to the music.

Home-movie footage of the band wandering about a desert plain in their Joshua Tree days provided entertaining visual accompaniment to "Where the Streets Have No Name."

Bright orange tongues of flame roared on the TV screens placed about the stage during "Bullet the Blue Sky," serving as a forceful visual representation of the lyrics: "Plant a demon seed/ You raise a flower of fire/ See them burning crosses/ See the flames higher and higher."

The separate stage in the crowd also gave intimacy to the enormous arena production. Donning a black flak jacket and Zoo TV cap, Bono stood alone on the smaller stage during "Bullet the Blue Sky," delivering his short, explosive attack on Central American civil war in military commando style.

He remained there for "Running to Stand Still," owning the spotlight in his dramatic portrayal of the agony of heroine addiction.

Throughout the concert, however, Bono refrained from becoming any more serious than the music required. His Zoo TV performance did not include any of his infamous political preaching or social sermons.

Though many critics and fans might welcome the change, Bono's new light-hearted attitude and pop-star posing seemed disturbingly incongruous with the heavy emotional quality of The Joshua Tree material. Bono almost began to reveal his social consciousness in his introduction to "I Still Haven't Found What I'm Looking For," but he carefully maintained the superficial Zoo TV front as he stated what he wanted to find: "An honest president, an end to this depression and a better TV station."

The March 13 Centrum stop on the Zoo TV tour also served as a birthday celebration for bassist Adam Clayton. In honor of Clayton's birthday, the band toasted him with champagne and led the crowd in singing "Happy Birthday," and a female "bunny-gram" bearing balloons adorned Clayton with bright pink boa and red wig.

The contrived gaiety of the spontaneous birthday celebration, so unlike U2, seemed curiously appropriate in the surrounding commercialism of Achtung Baby and the whole Zoo TV tour. In exploring new musical directions and casting aside its seriousness and social concerns for the new album and tour, U2 seems to have been desperate for something different. But for a band as popular with the critics and the public as U2, something different does not always mean something better.

The U2 concert at the Centrum could hardly be considered a failure, since their mere presence and the power of their music could save any show. Instead the performance was just a disappointment, something less than what one has come to expect from U2.