In San Francisco, where architecture is a spectator sport, you might think there would be a clearly defined set of guidelines spelling out how new buildings can best fit our distinctive surroundings.

You’d be wrong. But next year, that could change.

The City Planning Department has embarked on its first set of urban design guidelines, a two-year effort that has produced a 70-page draft. In many ways it is long overdue, making smart points that should be common sense. Yet the inherent subjectivity of such standards could muddy the waters rather than lead to better buildings, which is what we really need.

At the most basic level, the aim is “to promote the quality of individual buildings, and to enhance the experience of the city as a whole” according to the current draft, which is being presented to community and design advocacy groups.

“We see them as both practical and aspirational,” Jeff Joslin, the Planning Department’s director of current planning, said of the guidelines. “Right now, we have a vast amalgam of documents that speak to design, but none that approach it in a methodical manner.”

The new guidelines, if approved next year by the Planning Commission, would amplify rather than supplant such keystones of city policy as the Urban Design Plan that for the most part dates from 1971. It wouldn’t affect the low-slung residential districts of the city, which have their own guidelines, and it wouldn’t alter the height or bulk of what’s allowed in the neighborhoods and commercial districts covered by the new guidelines.

Nor is the focus simply on buildings.

There’s a section on site design, the way individual structures should fit into the city’s rugged topography and its cloak of large streets and tight alleys. “Public Realm” also gets its own section, including a call to “locate and design open spaces to maximize physical comfort and visual access.”

Inevitably, though, the flash points involve architecture.

Part of the problem is that no document can defuse the perennial tension between San Franciscans who want new buildings to look as if they’ve been here all along, and those who want the city to be a contemporary showcase on par with Barcelona or Rotterdam.

Take a statement as innocuous as “new buildings have the responsibility to sensitively respond to their context ... while being of their moment.” Some neighborhood watchdogs already have complained that the department wants to push modernism above all else.

Another red flag: a provision in the current draft for “waiver of design guidelines.” The idea is to make sure that spelled-out standards don’t “stifle innovation and/or exceptional design.” But the most conspiracy-fearing critics see the threat of an anything-goes loophole.

Don’t expect “waiver” to appear in the next version of the draft. “Maybe we should talk about ‘an exception for exceptionalism’,” Joslin said. “I’ll see how that flies.”

The notion of exceptionalism gets to a deeper issue.

Though guidelines are important, in an environment like San Francisco they can backfire. Standards that upgrade the sorriest proposed buildings also can be applied so joylessly and dutifully that imaginative architecture gets pressed into a predictable mold.

That’s not the intent here, but the current draft’s efforts to cover all the bases could lead to that result.

Remember the guideline that new buildings should “sensitively respond to their context”? Flip to the glossary, and we learn “the design context of a building may emulate, reinterpret, or contrast with its surroundings.”

There’s also a mixed message in the introduction to the architecture section. It informs us that “new projects should reinforce or enhance the physical patterns of neighborhoods ... with their own voice.” But the next paragraph stresses that contemporary additions should come with appropriate “massing, siting, scale, proportions, facade design, material choice and roof form.”

Uh-oh. Anyone who wants to second-guess a proposed project, or fiddle with the details, can find justification. The list of virtues becomes a checklist so vague as to be confounding.

To their credit, this isn’t the intent of Joslin and other top planners. They understand there needs to be room for innovation, the unexpected buildings or serendipitous spaces that soon feel right at home — the surprises that make you smile.

Joslin also emphasized that the idea isn’t to add yet another hurdle to a review process that routinely can stretch for years.

“There’s a lot of high expectation here (in San Francisco) in terms of design, but not a lot of clarity and certainty about how we review larger projects,” Joslin said. “We want principles that are more consistent and predictable” while still allowing flexibility.

The value of guidelines is that they can educate — even inspire.

With clear words and well-chosen images, lay people can get a sense of how specific aspects of a building or space can add up to something greater. Architects and designers can benefit from a cleanly focused primer on the values of a particular neighborhood or city.

That’s what is important, rather than fussing over style details or trying to be all things to all people. We need templates that all sides understand, not loopholes to be exploited.

If guidelines spell out a code of behavior that new buildings must meet, that’s a start. If they clear the way for architects to do their best possible work in our city, that’s even better.

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron

Information and workshop

For more information on San Francisco's proposed Urban Design Guidelines, go to http://sf-planning.org/urban-design-guidelines