This is a rendering of what a light-rail Purple Line train would look like running through the University of Maryland campus in College Park. (Maryland Transit Administration)

Maryland’s plan to build a light-rail Purple Line in the Washington suburbs would receive $125 million in federal aid in the fiscal year that begins Oct. 1, under the Obama administration’s proposed transit budget released Wednesday.

[Read The Post’s coverage of Maryland’s Purple Line Plan]

The rail project would receive federal money — the Federal Transit Administration has recommended a total $900 million for construction — only if the state finalizes a full funding agreement with the FTA. Under federal funding rules, that agreement would not be signed until the state has finalized the project’s estimated cost and secured the rest of the 16-mile line’s funding.

[Md. receives four proposals to build light-rail Purple Line]

However, the fact that the Purple Line remains in the FTA’s budget recommendation for a third year shows that it is still an Obama administration priority, even though Maryland officials have yet to announce a winning bid that will determine the project’s projected final cost. That announcement is expected sometime this month.

Gregory Sanders, vice president of the Purple Line Now advocacy group, noted that the $125 million in aid recommended for next fiscal year surpasses the $100 million included for the Purple Line in each of the two previous Obama administration budgets. Congress appropriated about $200 million, but the Maryland Transit Administration has not been able to spend it without the funding agreement in place. An FTA report released Wednesday said the MTA anticipates having a full funding agreement in mid-2016.

“The $125 million is not just a vote of confidence,” Sanders said. “I think a little more funding gets you a faster start. It gives Maryland a lot of flexibility to hit the ground running” to begin construction.

The new FTA report listed the Purple Line’s estimated construction cost at $2.45 billion and annual operating costs at $53.4 million. However, state officials had recently scaled back the project to an estimated cost of $2.15 billion.

State officials have cautioned that no numbers are final until the state awards a 35-year contract to a team of private companies that would finish the line’s design, build it over five years and help finance its construction. A private partner would then operate and maintain the line for 30 years. State officials have said they hope to begin construction this year and open the line to service in late 2021. The line would run east-west inside the Capital Beltway, between New Carrollton in Prince George’s County and Bethesda in Montgomery County.

[Will the money be there to build the Purple Line?]

Federal transit construction grants are increasingly competitive among cities and states vying for limited funds to expand rail and bus lines or build new systems to accommodate growth and spur economic development without significantly worsening traffic congestion.

The Purple Line retained its overall FTA rating of “medium-high,” even after the state cut some costs — one plan involves running trains less frequently in the opening year. That rating keeps it more competitive for clinching money than projects with “medium” ratings. The ratings are based on project costs and how they would affect local land use and economic development.

However, federal officials knocked the state’s estimate for the amount of growth it has assumed in Maryland’s transportation trust fund and the line’s operating revenue. In its report, the FTA said the growth predicted for both revenue streams “is more optimistic than historical experience.”

The FTA also said state officials’ estimate for the line’s construction cost “is toward the lower end of the range of what may be expected and is slightly optimistic.”

Asked about the FTA’s findings that the revenue and construction cost estimates were overly optimistic, MTA spokesman Paul Shepard said, “Any comment we would make would be premature until a [bid] proposer is selected.”

The FTA report said Maryland has committed to pay $484 million of the Purple Line’s construction from the state’s transportation trust fund, which would be about 20 percent of the total under the current cost estimate. A private partner would finance about $1 billion, or 43 percent, and the federal government’s $900 million would make up about 37 percent.

The Purple Line would run two-car trains aboveground, mostly along a three-mile recreational trail in Montgomery, and on local streets for the rest. The line would have 21 stations and connect neighborhoods with Metrorail stations and Amtrak and MARC commuter rail stations.

Supporters say it would provide faster and more reliable transit service than buses that become stuck in traffic. They also say it would serve a large number of transit-dependent residents and spark redevelopment around stations in aging inner-Beltway suburbs. Opponents say the project is too expensive and would disrupt neighborhoods along the route and destroy the parklike feel of a wooded recreational trail between Bethesda and Silver Spring.

[Hogan: Maryland will move forward on Purple Line, with counties’ help]

Maryland Gov. Larry Hogan (R) had balked at the project’s estimated construction cost but later changed course, saying he would build it if the state contributed less to a less-expensive project. The test will be whether any of the private bidders have offered a price that Hogan’s administration will accept.

Ben Ross, a longtime Purple Line advocate, said he is optimistic Congress will continue to appropriate the money that the FTA has recommended for the project.

“This is now a bipartisan project with Governor Hogan behind it,” Ross said.

The transit administration’s recommended $125 million, he said, “is a statement by the [Obama] administration that they consider this project on track and moving forward.”