Big-city ceilings

HOW high is up? For a major part of downtown San Francisco it's a 30-story limit for new structures. The same will be true for most of downtown Boston if a proposed plan is adopted.

These two cities may be signaling a welcome urban trend: making downtown growth more compatible with ``human values.'' The term embraces both tangibles and intangibles, such as the ability to find a parking place and the enjoyment of a city's historic character.

Both Boston and San Francisco are trying to do more than just limit the number of domineering, slab-sided skyscrapers. Economic and social factors make new approaches to urban development essential. In the past the main goal of planners has been to revive central-city economies. Growth of service industries provided need and justification for construction of large downtown office buildings. This coincided with the development of a modern architectural style using new structural capabilities to make the most of expensive downtown sites. The urban building boom brought new life to central cities. Now, that success has generated concern over ``livability.'' One result has been that residential use of remaining building sites is being given higher priority.

Imposition of building height and bulk restrictions, as well as design requirements, is not new. Strict guidelines have always guarded the architectural integrity of Washington, as well as its particular character. Historic Philadelphia and Charleston, S.C., early imposed limits on new buildings (though Philadelphia recently rescinded its restrictions). But there is a new imperative at work in urban planning. It is to make the new conform more to the old and cherished, and at the same time make urban d evelopers responsible to all city residents -- not just those who run the corporations, work in the office towers, or live in luxury housing. (New York, specifically Manhattan, is an apparent major exception.)

Thus, San Francisco has some new requirements that are more social than architectural. Developers must pay $1 per square foot toward toward financing day-care centers in the city. And Boston's proposed plan would provide a ``linkage'' system through which builders could win preference for highly desirable development sites by agreeing to undertake needed projects in outlying neighborhoods. Boston and San Francisco will probably have to do some fine-tuning on their new plans, and their approaches may not

be wholly suitable for other communities. But leaders of both communities are to be commended for their willingness to innovate -- and to take political risks for what they see as the long-range welfare of their cities.