Lincoln Center ceremonially broke ground yesterday morning on the first phase of its redevelopment, the socalled West 65th Street Project; unveiled plans for its second phase, the redesign of the approach to Lincoln Center from Columbus Avenue; and announced the finalists in the competition to redesign the Harmony Atrium, a currently depressed and little-used public passageway between Broadway and Columbus Avenue.

At a news conference after the groundbreaking – at which Mayor Bloomberg, Elizabeth Diller of the architectural firm in charge of the redevelopment, Diller Scofidio + Renfro, and the Juilliard graduate and fourtime Tony Award-winner Audra McDonald all spoke – the chairman of Lincoln Center, Frank A. Bennack Jr., announced that Lincoln Center has raised 75% of its $459 million share of the costs for the West 65th Street Project.

The project is already underway, and the public will start to see evidence of construction soon. The Paul Milstein Plaza, which extends over 65th Street and is a hangout for Juilliard students, will be destroyed, and a temporary footbridge constructed between the Rose Building and the plaza level by Lincoln Center Theater. This will eventually be replaced by a translucent glass footbridge.

The second phase of redevelopment, the Promenade Project, will create a much a much grander approach to the Josie Robertson Plaza from the street level of Columbus Avenue. Diller Scofidio + Renfro collaborated with FX Fowle to come up with a plan in which the car drop-off lanes will be submerged to the concourse level, allowing pedestrians to walk up a monumental stairway without dodging taxis or skirting the line of barriers that currently blocks the entrance to Lincoln Center.

“We believe Lincoln Center deserves a dignified entrance like other major civic and cultural buildings of New York,” Ms. Diller said in her speech. “It should have an extended threshold that transitions from the quotidian to the extraordinary.”

In just one of the many digital aspects of the redevelopment plan, the vertical faces of the new steps will feature L.E.D displays, offering upto-the-minute information on Lincoln Center programming. The plaza will be repaved with more durable materials, but its iconic appearance, including the central fountain, will re main largely unchanged.

The president of Lincoln Center, Reynold Levy, announced that Lincoln Center has reached an agreement with the owner of the Harmony Atrium to turn the underutilized passageway into a space that would link the many institutions of Lincoln Center and include a discount ticket booth offering same-day tickets to all of its venues. Mr. Levy named the two architectural firms in competition to redesign the Harmony Atrium: Morphosis, of Santa Monica, and Tod Williams Billie Tsien & Associates, of New York. One of the two plans – which were not available yesterday but were described by the architects in interviews – will be chosen this summer.

The plans seem to be quite different, with the Morphosis plan relying heavily on the high-tech digital displays that crop up elsewhere in the Lincoln Center redesign,and the Tod Williams Billie Tsien plan emphasizing more old-fashioned, physical experiences.

Thom Mayne, the founder of Morphosis and winner of the 2005 Pritzker Award – architecture’s Nobel Prize – described their plan as being “one smooth, fluid space of movement, part traditional architectural and part information.” Curved walls and ceilings would become surfaces for L.E.D., computer, and video displays. “The whole space is basically made up of information,” Mr. Mayne said.

Tod Williams Billie Tsien’s plan, by contrast, would create a space where a person could sit down for a glass of wine before going to a Lincoln Center performance. Mr. Williams and Ms. Tsien want to build the “world’s largest coffee table” – a 20-by-40-foot table made out of the same polished travertine as Lincoln Center’s main buildings. Visitors could sit at it (or on it) to have a bite to eat; for live performances, it would become a stage. They also want to create the “world’s largest solari board” – the kind of information board, with its distinctive clicking sound, found at train stations. The board would sometimes display Lincoln Center information, sometimes visual designs programmed by artists.

Despite the possibility for computerprogrammed designs, the Tod Williams Billie Tsien plan is decidedly lower-tech than the Morphosis plan. “What draws people to Lincoln Center is the ability to see people physically doing something, whether it’s dancing, playing an instrument, or singing,” Ms.Tsien said. “Especially in Times Square, there’s all these digital crawls and huge images on the side of buildings, and after a while you don’t see it anymore. We thought we would make something that’s happening physically – a sort of mechanical thing.”

In the course of the 65th Street Project, the Alice Tully Hall box office will be closed for much of the summer, as construction takes place for an expansion of Alice Tully Hall and Juilliard.

Some Juilliard dance students eating lunch on the Milstein Plaza yesterday were slightly disgruntled about its destruction, and about the construction in general, which they will graduate too soon to enjoy the benefits of.”It’s a communal space where people just hang out or eat lunch,” explained ArikaYamada, a second-year student.

“We don’t really have a campus, so this is the only place to meet, or if we have a 30-minute break between classes, to come and get outside for a little bit,” said Brett Perry, a third year student.

Asked if she was mollified by the promise of a new green for Juilliard students, Ms. Yamada said, “Yeah, if it’s a huge green field. But I also heard that there’s going to be restaurants and all these commercial things underneath.” (The green will be the roof of a new restaurant.)

“I don’t really like the architecture [of the redesign],” Ms. Yamada said. “I really like this classic architecture – it’s historical, it’s a landmark.”

Both she and Mr. Perry, though, were aware that future Juilliard students would enjoy several benefits, including more studio space and locker rooms, wireless Internet, and a new, glass studio visible from Broadway.”The process is not going to be that fun, but the finished product is going to be cool,” said Mr. Perry. “I’m really excited about the studio that’s going to overlook Broadway, so that people from the street can look up and see us take class.”

Meanwhile, work began Friday on the construction of two new studios for the School of American Ballet, in the Rose Building. The design of the new studios, which are essentially glass boxes steel-cantilevered to “float” over existing studios,are also the work of Diller Scofidio + Renfro.

SAB had been looking for a way to build a new studio above one of its existing double-height studios for some time, but hadn’t come up with a plan that worked. When Ms. Diller saw the space, she immediately visualized what had to happen. “Peter [Martins, faculty chair of SAB and ballet master of New York City Ballet] and Liz [Diller] walked into the studios, and she just saw it right away,” said the executive director of SAB, Marjorie Van Dercook. “She said, ‘Oh they have to float.'” Ms. Diller’s glass-box design meant that both upper and lower studios could have natural light. “When she showed us the model, we decided to do two new studios instead of one, because it was so exciting,” said Ms. Van Dercook.