America's Bridges

''Stubborn Bridge,'' reads the headline in the newsletter of the Society of Industrial Archeologists (SIA). The subject: a mighty midget of a bridge at Bellows Falls, Vt., which shrugged off four blasts of dynamite before cutting torches brought it down last summer.

Another SIA headline shouts: ''Bridge Rescue a Popular Cause in Ashtabula, O.'' The tale told how an Ohio city councilman's plea to save the ''Mystic type of Brown bascule bridge'' helped him to win an election.

Bridges have long had their admirers. Just look at the five-year effort begun in 1978 to inventory the nation's historic bridges; the Preservation Bridge Forum sponsored by the National Academy of Sciences; and even the rather lackluster annual awards by the steel-and-concrete people.

Recently, however, news stories decrying the state of the nation's bridges haven't helped the structures' public image. The collapse three weeks ago of a Connecticut Turnpike bridge in Greenwich underscored such concerns. But appreciation of the artistry in bridge building - the symbiosis between form and function - remains on firm ground. The notion that a bridge is more than the shortest distance between two sides of an obstacle has energetic allies.

Some of them focus on ''bridge aesthetics'' - exemplified in the centennial of the Brooklyn Bridge. Lewis Mumford's ode to that famous span strikes the keynote: ''In this structure the architecture of the past, massive and protective, meets the architecture of the future, light, aerial, open to sunlight, an architecture of voids rather than solids.'' Others pay attention to the ''bridge anthropomorphics'' of those who assign human characteristics to the structures. That ''structurally unsound'' bridge in Bellows Falls was applauded for its plucky endurance.

Safety, certainly, has to take precedence over architectural nobility. But some bridge partisans worry that superficial attention to safety may threaten this majestic, and often ethereal, form of industrial art. Their concern: Will a fleet of look-alike spans, kin to the endlessly similar superhighways they serve, create a boring 55-mile-an-hour landscape?

The problem arises, say observers, because the Federal Highway Administration (FHwA) pays for 80 percent of new construction, but nothing for maintenance of old structures. The financial incentive, therefore, is to demolish, not rehabilitate - or, as preservationists say, recycle.

Nicholas Westbrook, curator of exhibitors at the Minneapolis Historic Society , calls it a ''conflict between the laudable desire to restore the nation's deteriorating infrastructure and the equal social good of preserving our built environment.''

Mr. Westbrook mourns the recent loss of his city's High Bridge. He is now trying to save the Broadway Bridge, a splendid 1887 wrought-iron structure paired with an equally handsome 1895 granary.

''Bookkeeping chicanery'' is the way Westbrook describes the public financing process by which older bridges across the nation give place to new ones costing four times more. He feels that ''free'' federal money invites greater expenditure. Thirty years ago, by contrast, tight budgets encouraged imaginative repair of the Minneapolis Broadway Bridge.

But Bruce Eberle, archeologist for the FHwA, argues that a superficial or mindless passion for asphalting America does not characterize the current approach to our bridge heritage.

''Every bridge that appears to be historic will be considered,'' he says, citing the inventories under way in a majority of states. ''They have to show that they can't be repaired before they are replaced.''

But bridge aficionados aren't convinced. Eric DeLony, architect of the Historic American Engineering Record for the National Park Service, goes so far as to argue that FHwA criteria for widening bridges produce, almost by definition, more dangerous bridges. A narrower span - one holding two lanes, not four, and slowing traffic to 20 miles an hour instead letting it plunge ahead at 50 - is inherently safer, he says.

Mr. DeLony has also gathered case studies to show how saving beautiful or historic bridges can mean saving money. The Second Street Bridge in Allegan, Mich., he says, is ''a classic (case), with the local population convincing the city to save the bridge, the engineering firm of Wilkins & Wheaton of Kalamazoo doing a 'brilliant rehab,' and the community celebrating last month with a 'bridgefest.' ''

Then there's the Pasco-Kennwick Bridge, spanning the Columbia River between Washington and Oregon. Preservationists brought suit to keep the old bridge open for bikes and pedestrians. An appellate court judge has declared that the highway people failed to investigate thoroughly the alternatives to demolition. The judge has halted, for now, plans to destroy the bridge.

Such cases may increase public awareness of the preservation cause - not only of the historic and environmental arguments, but also of the economic one. At present, that awareness varies from city to city.

''This is a big bridge town,'' says William Rudman of the Cleveland Foundation, which helped inventory that city's pioneer metal bridges. ''There are wonderful bridges, and the mood has always been they must be kept up.''

Thomas Thompson of the Minnesota Historical Society sees a serious lack of care for the historic concrete bridges that span the twin cities of Minneapolis and St. Paul. ''We trundle back and forth across the Mississippi, and, really, people don't pay a lot of attention,'' he says.

Meanwhile, complaints that older bridges restrict traffic flow persist - a legacy, doubtless, of the 'automania' that says such flow is America's most important function. When the federal government calls 200,000 of the nation's half-million bridges ''inadequate,'' its criteria are likely to include inflated claims of the need for wider bridges as well as concerns about structural weakness.

Combine the urge for an ever-grander highway system with legitimate concerns about safety, and we may well see more monotonous new bridges squeezed out of the federal interstate tube - more standardization, more homogenization of the public architecture.

The need, says architect DeLony, is for wider recognition that bridges ''are just as important as buildings as far as what this country is about.'' The fact that America's bridges are now resting over troubled political waters should make caretakers of the built environment take a longer, deeper look at them.