Architects unveiled the designs for three office towers at the World Trade Center site Thursday, including a skyscraper topped by four shining diamonds that would light up lower Manhattan at night.

The buildings, designed by architects Norman Foster, Richard Rogers and Fumihiko Maki, will join the 1,776-foot Freedom Tower around a transit hub and facing a memorial to the victims of the Sept. 11, 2001, terrorist attacks.

The three will be smaller than the Freedom Tower and descend in height in a semicircle around the memorial. Inside, they will have floors specifically for financial trading, plus offices and shops to replace the former trade center.

"Each design is timeless in its feel and reflects the individual genius of each architect," said developer Larry Silverstein, who commissioned the plans. "At the same time, the towers relate perfectly to each other visually and, together, will enliven the surrounding area with a dynamic, retail-oriented streetscape."

The concept designs for the three towers are still subject to alteration, but they aren't expected to be significantly overhauled as initial designs for the Freedom Tower were due after officials raised security concerns.

The Freedom Tower, memorial and transit hub are already under construction. Construction on the three new towers is to begin in 2007 or 2008 and wrap up in 2012.

The largest of the three is a 78-story tower with a roof sliced into four diamond shapes. It was designed by Foster, who used the diamond pattern in the new Hearst Tower in New York. The diamonds would be lit at night, casting light onto the planned memorial pools.

Rogers proposed a slender, 71-story tower with crisscrossing beams down the sides and topped with 100-foot spires at each corner.

Maki's 61-story tower, sporting two different elevations, would be clad in a perforated aluminum that would make it the lightest-colored of the three. It also would have a restaurant and bar with panoramic views of the memorial.

The towers would return more than 6 million of the 10 million square feet destroyed on Sept. 11.

In addition to the towers, a performing arts center is planned, although there is no construction schedule, budget or released design for it. The city agreed Thursday to take over planning for the center, saying it would help ensure it gets built.