HO CHI MINH CITY Like to wallow in nostalgia and Old World charm? If so, East Asia can be a frustrating place. Its cities breathe vibrancy, but sometimes at a cost to their souls - and the ambience. Here in Saigon, the gaudy and just slightly seedy crown-topped Rex Hotel is still around to tweak the memories of America's Vietnam veterans. But you don't have to hanker for the days of South Vietnam to fear for the future of Don Khoi Street, known back then as Tu Do Street. This slim but elegant tree-lined avenue at the very heart of old Saigon was until not so long ago a mix of two-to-eight story buildings and some very ordinary shop houses. A few, such as the 1930s Grand Hotel, were actually stylish. The importance was not so much the architecture but the scale. But now one whole block of Dong Khoi, not to mention an elegant little mosque, is overwhelmed by the 25-story concrete masses of the Sheraton and new Caravelle hotels. These monster buildings are not improved by their shops, those international symbols of fickle fashion and transient wealth: Prada, Bulgari, Dolce & Gabbana, etc. Further down Dong Khoi toward the Saigon River a row of low-rise shops and restaurants has just been demolished. It's not clear what will go up there. In Ho Chi Minh City, plot ratios and building heights are matters for negotiation, not known rules. Transparency is not a feature of city government in a one-party state. But the betting must be on another 25-plus story concrete slab. It is not that the city center does not need new offices and hotels, but densities could easily be increased by redevelopment within the existing scale with a maximum height of, say, 25 meters. But the way things are going, the old center will gradually become a mass of close-packed concrete, dwarfing its streets and overwhelming its infrastructure. Meanwhile, plans to expand the city to the palm groves and paddy fields across the Saigon river are making very slow progress. Hanoi has been luckier. Thanks to its position as capital and the pleadings of outsiders, the scale and many buildings of its French colonial center look likely to be mostly preserved. Saigon never had the architectural unity of Hanoi, but it had scale and a few fine buildings. But commercial forces, lack of planning and corruption seem likely to make Saigon follow the Bangkok or Hong Kong path of urban development: Unrelieved concrete and massive towers constructed to maximize space and rents. There are in fact many better examples in East Asia. Tokyo has been a model of redeveloping within an established scale and focusing high-rises in a few areas well served by transport. Seoul has established new business and government districts outside the old center - and even turned its central square from a giant traffic intersection into a park. Even Taipei, not the prettiest city in Asia, has moved its business center to an area that now boasts the world's tallest building, in one of its most earthquake prone capitals. Kuala Lumpur left its old commercial and colonial era government buildings mostly intact and built its skyscrapers on green field and suburban sites. It is questionable whether one of Asia's smallest capital's needed what was until recently the world's tallest building. But at least its Petronas towers are an exciting piece of architecture. Singapore realized just in time that the old buildings and their refurbishment have helped liven up the city and provide a tourist attraction. Singapore has proved, too, that rapid development and intelligent urban planning are compatible. So, maybe there is still some hope that the People's Committee that runs Ho Chi Minh City - and itself inhabits an ornate colonial-era building - will recognize before it is too late to look at some more effective Asian models to leave an elegant, livable and economically viable city for the people of the future.