The National Park Service (NPS) today announced the initiation of a General Management Plan/Environmental Impact Statement (GMP/EIS) process for Jefferson National Expansion Memorial (commonly referred to as the Gateway Arch).

In the dry prose of a press release issued Friday comes a magnificent opportunity for St. Louis. For the first time in 48 years, the National Park Service has opened the door a crack. It is willing to listen to ideas for changing the way it manages the 91 acres that surround the Gateway Arch.

There are those who will say the Arch and its grounds are perfect the way they are. This is how Eero Saarinen imagined it in 1947 and 1948: 630 feet of catenary-curved stainless steel rising from a faux forest primeval, a museum of westward expansion tucked below it, walkways and reflecting ponds, a stairway descending to the Mississippi River.

John C. Danforth respectfully disagrees. The Arch itself is magnificent, he says, but it is only one piece of the picture. The grounds to its north and south are underused. To its west, the six lanes of Memorial Drive and six lanes of below-grade interstate highway sever the connection between the Arch and the city. To its east is the Mississippi, but the riverfront is ugly and barren. On a good day, you might see a dead carp.

The Arch, Mr. Danforth says, deserves better. So does St. Louis.

“This is not like Yosemite,” Mr. Danforth said. “We’re not saying, ‘Hey, let’s improve Yosemite.’ This is a man-made mess.”

The former Republican senator from Missouri is haunted by the view from his the window of his law office in the Metropolitan Square Building: the all-but-empty Arch grounds, the scraggly riverfront, the depressed highway lanes.

“What we’re saying is that if it’s possible for humankind to build something magnificent, and if it’s then possible for humankind to make it ugly, then it should be possible for humankind to make it not only good, but great,” Mr. Danforth said.

The view gave rise to a vision: the depressed lanes bridged by a three-block landscaped lid; the areas directly east and west of the Arch itself (the “viewshed,” in architect-speak) protected and pristine, but the northern and southern reaches of the Arch grounds transformed into welcoming, visitor-friendly space. A “world-class” cultural attraction is built. Restaurants, pathways and interactive displays reach out and embrace the riverfront.

It takes a long time to turn a vision into reality. It will be remembered that the vision that became the Arch began with a rigged 1935 referendum to approve the issuance of land-clearance bonds. Despite the controversy, President Franklin D. Roosevelt signed legislation authorizing a Jefferson Westward Expansion Memorial. Mr. Saarinen won the design competition in 1948, but the Arch wasn’t completed until 1965. Mr. Danforth, 71, doesn’t have 30 years to wait.

He and his brother, former Washington University chancellor William H. Danforth Jr., 82, are willing to spend what’s left in the Danforth Foundation on the project, Mr. Danforth said, “but if we’re talking walkways and kiosks, we’re not interested. We’re talking about the legacy of our family. If we’re going to do it, let’s do it big. Let’s do it big and world-class.”

Mr. Danforth has been frustrated before when he tried to talk St. Louis into doing something big. His “St. Louis 2004” project, designed to infuse regional projects with the same kind of enthusiasm that gave rise to the 1904 World’s Fair, fell far short of the goal. The Arch project is more narrowly focused.

It begins with a Park Service process, collecting ideas for what might be done with the Arch grounds. These might be limited — a kiosk here, a restaurant there — or they might be as expansive as Mr. Danforth and his allies imagine. Last summer, a panel of three civic leaders appointed by Mayor Francis Slay to consider the future of the riverfront reported that without Park Service cooperation, riverfront redevelopment would be impossible.

Reason: The river is too big and unpredictable to allow for development along its edges. That means the Arch grounds would have to be involved. Merely bridging the depressed lanes of I-70 would involve a grant of a few acres from the park service for construction, ventilation and service facilities.

So the Danforth Foundation asked the three members of the panel — Peter H. Raven, director of the Missouri Botanical Garden; Robert Archibald, president of the Missouri History Museum; and Walter L. Metcalfe Jr., senior counsel at Bryan, Cave law firm — to come up with recommendations.

The panel discovered that according to the Park Service’s figures, 27 percent fewer people visited the Arch grounds in 2006 than in 2001. Attendance at other tourist attractions either increased slightly in the same period or remained static.

What was needed, the panel concluded, was a major new “destination” attraction for the Arch grounds. Just what it might be is an open question — Mr. Archibald suggested a museum devoted to American migration, sort of a domestic version of Ellis Island — but the idea is to make a visit to the Arch grounds “more than just a photo-op,” Mr. Metcalfe said.

“We asked ourselves what will keep out-of-town visitors here for one more night,” he said. “If we can do that, we pay for the whole thing.”

The new attraction should be of international significance, with its design, scope and quality consistent with that of the Arch itself, the panel agreed. It would be operated and maintained by a regional not-for-profit trust.

The panel polled 1,100 residents of St. Louis and surrounding counties. On the question, “Do you favor or oppose efforts to develop the Gateway Arch grounds to the north and south of the actual Arch to provide a variety of cultural, recreational and leisure activities and entertainment?” more than three in every four people — from every part of the region — said they favored the idea.

The panel obtained the endorsement of the broad outlines of the plan from political, civic, labor and business groups in the region. Now it hopes to push its ideas through the crack in the door that the Park Service opened last week. Its self-imposed deadline: 2015, the 50th anniversary of the completion of the Arch.

Much remains to be done: soliciting other ideas, public comments, environmental impact statements, design competitions, perhaps even an act of Congress. But the Park Service has cracked the door. St. Louis must shove through it.

It is manifest that St. Louis exists because of its location at the confluence of the nation’s two great rivers. This editorial page long has argued that the neglect of the riverfront is absurd and self-destructive. We believe the Arch is the region’s greatest man-made treasure. We believe that the ugly highway gash that divorced the city from the river that gave it birth is a mistake that must be bridged.

We further believe, with Mr. Danforth, that too often St. Louis suffers from a lack of boldness and civic imagination. And we believe, with the poet Browning, that “a man’s reach should exceed his grasp, else what’s a heaven for?”