Memorial Bridge needs a major overhaul. (Marvin Joseph/The Washington Post)

The Arlington Memorial Bridge, a symbol both of American ingenuity and the nation’s sagging infrastructure, has received a $90 million grant for a massive reconstruction project, officials said Tuesday.

The infusion of federal dollars marks a major step toward restoring the deteriorating bridge, but it does not fully fund the project, which the National Park Service has estimated will cost $250 million. It is not clear where the rest of the money will come from, although the Park Service could seek additional federal money.

Park Service Director Jonathan B. Jarvis said the bridge, which carries 68,000 vehicles a day, will need to be shut to traffic in 2021 if the overhaul is not done. He said it would turn into a “footbridge.”

The span is one of more than 58,000 “structurally deficient” bridges across the country, according to federal figures.

The Park Service alone says that nationwide, it has a backlog of about $6 billion in transportation-related fixes that need to be made.

The agency nearly bungled the opportunity for the U.S. Department of Transportation’s FASTLANE grant program this year, officials said; flawed coordination with local jurisdictions almost led to the Park Service’s missing the application deadline for the grant. But last-minute pressure by congressional representatives and an agreement by the District to co-sponsor the application helped get the necessary paperwork filed just under the wire.

In the end, the project received more than 10 percent of all the funds awarded nationwide under the highly competitive FASTLANE program, which has $800 million in funding in 2016.

The Memorial Bridge, which connects the entrance of Arlington National Cemetery in Virginia to the Lincoln Memorial in the District, faced a series of embarrassing restrictions after engineers concluded that the steel beams helping to hold up its deck “no longer meet load-bearing standards.”

Commuter and tour buses have been diverted from their more obvious, direct route over the Potomac River, given concerns that having them rumble across the span could speed up the bridge’s deterioration. Members of Congress have alternatively dubbed the state of the bridge “embarrassing,” “outrageous,” and a symbol of “failed leadership” by Congress and the federal government more broadly.

“This significant federal investment will go a long way towards ensuring that Memorial Bridge remains open, which is welcome news for the region’s commuters,” said a joint statement from Sens. Mark R. Warner (D-Va.) and Timothy M. Kaine (D-Va.), Del. Eleanor Holmes Norton (D-D.C.), and Reps. Barbara Comstock (R-Va.), Don Beyer (D-Va.) and Gerald E. Connolly (D-Va.). “This would not have been possible without the crucial support of Mayor [Muriel E.] Bowser and the District Department of Transportation.”

But some sticky details remain, including whether local jurisdictions will be willing to reach into their budgets to help make up the difference.

According to congressional figures, the Park Service needs to find $36 million in matching funds for the $90 million federal grant. That can include other federal money as long as they are not transportation funds, officials said. Or it might include local funds.

A District spokeswoman could not immediately clarify whether the city would add money to the effort.

The rehab project will come in two parts, according to a congressional breakdown. The first phase will “focus on the approach spans, which are the most in need of repairs, at a total cost of $166 million,” according to the delegation’s statement. Those fixes will allow the bridge to stay open until 2030. The rest of the project — and money — would go toward a second phase to rebuild corroded drawbridge components, according to the statement.

Jarvis said last year said that the bridge is safe but that its innards are essentially a deteriorating “erector set.” Time, plus dripping water and road salt, have speeded the decline.

The bridge was dedicated in 1932, and the drawbridge was last opened in 1961, according to the Park Service. It was once the longest such levitating span in the country, with five million-pound counterweights that helped control its movements.

Park Service spokesman Jeremy K. Barnum called the grant a welcome development. “Obviously, it’s great news,” he said. But he had no immediate comment on how the Park Service will find the additional money needed for the job.