The wavy paving was the idea of the architect Wallace K. Harrison, who had admired a similar design at the Copacabana Beach in Rio de Janeiro, wrote Carol Herselle Krinsky in ''Rockefeller Center'' (Oxford University Press, 1978).

Harrison thought the pavement could enliven an otherwise straight-edged building, Ms. Krinsky wrote, and hoped to link the outside and inside by extending the distinctive pattern from the plaza to the lobby.

Unfortunately, the smooth terrazzo proved treacherous outdoors; slippery in the rain and nearly blinding under sunshine. Beginning last year, the plaza paving was replaced with a rougher terrazzo. Workers from the Port Morris Tile & Marble Corporation in the Bronx used templates to recreate the pattern.

Port Morris, a fifth-generation company run by the DeLazzero family, was the original paving contractor. The inside floor has lasted so well that it needs only to be washed, honed and polished.

''The best of the postwar buildings were built out of materials and using detailing that is equal if not better than the best of the Beaux-Arts buildings,'' said Ms. Paulsen, the landmarks chairwoman. ''This lobby was built for the ages. Not just the bossa nova.''