Mission Impossible? There are big doings under foot at Times Square. And all of them are to be accomplished without a disruption of train or street traffic.: [CITY Edition]

HOWARD J. COHEN has a dream: rich red granite walls, gleaming steel columns, vast forest green slate floors with white marble trim and sunlight streaming through three stories of glass blocks.

Daniel W. Greenbaum has a nightmare: skyscrapers plunged into darkness, businesses bereft of telephones, broken water mains flooding the theater district and ceilings collapsing on trains.

Cohen, of William Nicholas Bodouva, is the chief architect and Greenbaum, of Vollmer Associates, the chief engineer in an effort to build the world's finest subway station beneath Times Square, crossroads to the world.

"Howard's job is to make it beautiful and practical," Greenbaum said of what both men claim is the most ambitious subway station project in history. "My job is to see that Times Square doesn't fall down."

The task is herculean.

Right now, the Times Square subway station squeezes 200,000 passengers a day through a tangle of dark, narrow, urine-soaked corridors. Because half of this traffic is arrivals and departures and the other half transferring between lines, the groups shove in opposing directions, often backing up onto the street on the narrow stairwells. And the proposed 42nd Street Rede- velopment Project, scheduled to begin late next year, is expected to draw an additional 50,000 daily subway riders into the station by the end of the century.

The Transit Authority and the private real estate developers backing the project are coughing up $87 million to expand the station's capacity by 25 percent. The catch is, there's no room to build beyond the existing boundaries.

Undaunted, the design team of 20 architects and engineers has come up with a plan that requires them to:

Gut and rebuild the vast station, but without disrupting service on four major subway lines.

Raise an entire block of Seventh Avenue by one foot without obstructing the more than 26,000 cars, taxis and trucks that trundle through each day from 41st Street to 42nd Street.

Relocate a 48-inch water main, 28 telephone cables and 120,000 pairs of Con Ed wires under Seventh Avenue that will have to be moved one by one to avoid Midtown blackouts. "You can't believe the amount of spaghetti that's under there," Greenbaum said. "This is the biggest shift...