Cyclists use the bike lane along New Hampshire Avenue in Washington, D.C. (NIKKI KAHN/THE WASHINGTON POST)

The looming Capitol Hill battle over transportation priorities in a budget-slashing era may have found its lightning rod issue: bike paths, pedestrian walkways and wildflowers planted by the side of the road.

The question is this: With the nation facing a transportation crisis that has gotten little attention outside of policy wonks and Washington, should the federal government continue to mandate that states spend federal dollars on pedestrian safety, bicycling trails, landscaping and historic preservation?

Like many of the issues that get marquee attention in the partisan warfare in Congress, its symbolism outweighs the actual expense. And singling it out brings to the fore substantial philosophical differences over how to target transportation dollars and to what degree Washington should be allowed to set state priorities.

“When you have 69,000 bridges in the country that are at risk and we’re saying ‘Don’t fix this bridge but build this museum,’ it tells you Congress has lost its priorities,” said Sen. Tom Coburn (R-Okla.).

In September, Coburn briefly held up an extension of transportation funding because he objected to requiring states to spend federal dollars on projects that don’t “enhance their safety or their ability to commute.”

“I know priorities are in the eye of the beholder, but what we lack is common sense,” Coburn said. “And we lack more of it here [in Washington] than we do in any state capital, and state capitals lack it compared to city governments.”

The federal transportation enhancement program governed the spending of $927.5 million federal dollars in fiscal 2011, about 2 percent of the total $40.2 billion highway budget. Between the program’s inception in 1992 and 2010, states used $8.7 billion in enhancement funds, about 84 percent of the money made available.

“This program has been the lifeblood of the nation’s trails, biking and walking programs,” said Kevin Mills, vice president of the Rails-to-Trails Conservancy. “It’s wildly popular across the country.”

Locally, the money has gone toward building a bike and pedestrian bridge over Veirs Mill Road at Aspen Hill Road; restoring locks and the adjacent towpath of the Chesapeake & Ohio Canal; restoring the buffalo sculptures on the Dumbarton Bridge and the lion sculptures on the Taft Bridge; transforming an abandoned rail line into the Capital Crescent Trail; and building bridges to carry the Bethesda Trolley Trail over I-270 and I-495.

Advocates for the funding mandate say they will fight to preserve it, but they may already have lost the battle. House Transportation Committee Chairman John L. Mica (R-Fla.) said it won’t be included in the long-term funding bill he expects to produce this fall. And Coburn said he has received assurances on the Senate side that the spending will be made optional rather than mandatory.

“I was promised that there would be a flexibility so that states that needed to use that enhancement money on other things could use it on other things,” he said.

But Mills and other mandate supporters are counting on the more than 160 members of the bipartisan Congressional Bike Caucus to take up their cause.

This disagreement is taking place on a much larger stage, as Congress faces a gargantuan gap between resources and needs. The immediate debate this fall is over how to shape long-term transportation funding that most likely will range between $45 billion and $54 billion a year.

But that discussion in haunted by repeated credible warnings that U.S. transportation systems — highways, the rail network, aviation, ports, mass transit — are worn out, outdated and need investment well in excess of a trillion dollars.

One study put the figure at between $134 billion and $262 billion a year, while another, released last week, said that postponing that investment could inflate the cost to $5 trillion by 2035.

A 2010 report by 80 transportation experts led by two former U.S. secretaries of transportation, Norman Mineta and Samuel K. Skinner, concluded that “Winning public support . . . will require policy makers to unite behind a compelling vision for U.S. transportation policy.”

So far, Congress is united only in agreement that there is too little money to fund transportation. The first skirmish has come over bikes and begonias, but there will be scores of others if a transportation bill is to pass by early next year, the target set by Mica and other congressional leaders from both parties.

“They think the only federal role is interstate highways, but virtually every community out there wants a balanced transportation program,” Mills said. “They put landscaping in the category of frivolous spending. But wildflowers along the highway contribute to erosion control, and if you ask the states, they’ll tell you it saves them a whole lot of money on mowing.”

The $3.4 million mini-tunnel that gives turtles safe passage under a Florida highway, which Coburn cited as an example of extravagance, finds defenders who say it saves motorists from deadly collisions that occurred when they swerved to miss the crossing turtles.

Mica and Coburn say that in tight times, the states — not Washington — should decide how their federal funding is allocated.

Whose money is it? Who decides?” Coburn asked. “We’re building museums, we’re building squirrel crossings. We’re doing all these things that, if we had extra money, if we were running a surplus, sure, nobody would really be complaining about it.”

But faced with an enormous federal debt and huge transportation needs, he said, “We can no longer have silly priorities get in the way of real needs.”

“I guarantee you that I don’t know where the number one dollar priority ought to be in Oklahoma, but I also guarantee you that the director of Oklahoma’s highways does,” Coburn said. “Let’s let him have the freedom to do what’s best for Oklahoma.”

Oklahoma spent $142 million on hundreds of projects under enhancement program guidelines between 1992 and 2010. Most of the outlays were under $1 million. Those that cost more than that included construction of several welcome centers; trackside and depot improvements for Amtrak in Oklahoma City; a harbor project in Muskogee; and $2.5 million for the Cross Timbers Ancient Forest Preserve in Osage County.

“We picked the best projects we could,” said Gary Ridley, Oklahoma’s transportation director. “But we have a great need for [funds to fix] structurally deficient bridges in the state. Certainly that’s where our focus is, and it always has been. It does make it difficult when you have mandatory programs dictated by the federal government when you know your money should probably be spent in other areas that are more critical.”