An architectural rendering of what the Maryland Transit Administration says a Purple Line station would look like in downtown Bethesda. (Courtesy of Maryland Transit Administration)

Officials with the Federal Transit Administration are seeking Congressional sign-off on a funding agreement that will clear the way for major construction on Maryland’s Purple Line light-rail project to begin later this year.

Congress has 30 days to review what is known as a Full Funding Grant Agreement (FFGA), essentially the government’s guarantee to contribute to the project. Once that review process is complete, it will be sent back to the FTA administrator for her signature.

Those actions ensure that the $900 million the federal government pledged to the 16.2-mile light-rail line will come through. The federal funds will cover nearly half of the estimated $2 billion it will cost to build the line.

“The Full Funding Grant Agreement (FFGA) for the Maryland National Capital Purple Line project has been sent to Congress for the required 30-day review period,” FTA said in a statement.

But federal officials declined to offer any specifics, including whether they insisted on any changes to the contract state officials signed with the group that will build and operate the line as part of a 36-year public/private partnership. Although the agreement sets out an annual payment schedule, they would not say whether there were any changes in the financing structure of the project.

Until Congress signs off on the deal, “FTA cannot comment further on the issue. More information will be available at that time,” FTA officials wrote.

Maryland state transportation officials also were tight-lipped, referring all calls to the FTA.

Even so, approval of the grant agreement is an important milestone because it clears the way for major construction to begin.

“We’re assuming that it’s a done deal,” said Roger Berliner, vice chairman of the Montgomery County Council. “There’s been such cynicism about government’s capacity to do anything big so for us to be able to point to something where dirt will be dug and something will be built – it’s nice. Should it take this long? No. But when it happens you have to be grateful it’s done.”

The Purple Line is a 16.2-mile light-rail line that will run along a recreational trail and local streets between Bethesda in Montgomery County and New Carrollton in Prince George’s County. The east-west line will provide a vital rail link between two of Maryland’s biggest counties and will connect the state’s Metrorail lines with Amtrak and MARC commuter rail stations. It have 21 stops, including Silver Spring, Langley Park, the University of Maryland and Riverdale.

In April, Maryland Transportation Secretary Pete Rahn signed a contract with Purple Line Transit Partners, the consortium that will build and operate the light-rail line as part of a 36-year private/public partnership. But state officials could not allow crews to begin the bulk of the work until the federal grant agreement is finalized.

Congress already has appropriated roughly $203 million for Purple Line construction.

Of that amount, $3 million has been awarded to the Maryland Transit Administration as part of a grant in 2012 for preliminary engineering and environmental impact study activities. The remaining $200 million in appropriated funds will be released when the agreement is signed.

President Obama’s proposed FY17 budget includes a recommendation for a next installment payment toward the FFGA of $125 million.

Even though the money is “guaranteed,” Congress must still make an annual appropriation each year. Once the grant agreement has been approved, however, it is rare that the money would not be made available.

Officials on other light-rail projects say a federal funding agreement gives developers the certainty that they -- and their banks -- are seeking before they invest in building new apartment or office buildings around future stations. The agreement, they say, assures developers that a light-rail line in plans for years will actually get built.

Tina Votaw, a transit-oriented development specialist for the Charlotte light-rail system, said she heard from developers occasionally as the first 9.6-mile segment of the city’s light-rail Blue Line was being planned. After the project’s full funding grant agreement was signed in early 2005, she said, developers’ calls picked up.

Like the Purple Line, Charlotte’s Blue Line was designed not only to move people but also to spur economic development around stations.

“The phone started ringing pretty much continuously,” Votaw said. “Developers said ‘Now you’ve got the [federal] money. It’s going to happen. Now we’ll make the investment.’”

Purple Line Transit Partners is led by Texas-based Fluor Corp., the French investment firm Meridiam and Star America, a New York firm that invests in public infrastructure projects.