THE FAILURE of modem architecture and modern sculpture as pub- lic arts was once well expressed by Sir Denys Lasdun when questioned after a lecture. Asked if he had ever contemplated using sculpture to relieve the possible monotony of the shuttered concrete walls of his National Theatre in London, he replied that he had:  had thought of putting a Henry Moore at the end of Waterloo Bridge-the opposite end of the bridge from the theatre on the South Bank. It was a profoundly depressing response, because it confirmed what is evident in all modern cities: that architects and sculptors do not know how to work together. It was not just arrogance that made Lasdun dismiss the idea that sculpture could in any way enhance his building. Modern architects conceive of buildings as monumental abstract sculpture-triumphantly so in Lasdun’s case-while sculptors consider their work in isolation, as having value only in purely formal terms.