WASHINGTON — A battle is brewing over federal funding not only for Metro but also for the proposed Purple Line light rail project.

President Donald Trump proposed last week to slash the federal transportation budget by 13 percent. And the construction of the Purple Line — with a projected price tag of $2 billion — is dependent on nearly $1 billion in federal funds.

Following the proposed 2018 budget, transit plans that don’t have a signed federal funding agreement “would be funded by the localities that use and benefit from these localized projects.”

This could endanger the planned light rail route since state and local officials contend they can’t carry the cost alone.

Proposed budget cuts would endanger Metro funding and many other transportation projects nationwide that Montgomery County Council President Roger Berliner expects to see a bipartisan fight in Congress to save them.

“I am hopeful that we will prevail — both with respect to the Purple Line and ultimately with respect to Metro,” he said.

The Purple Line project would run 16.2 miles from Bethesda to New Carrollton and would connect with four branches of the Metrorail system, as well as all three MARC commuter rail lines and Amtrak.

The line was scheduled to begin construction in late 2016 and open for service in 2022. But construction remains delayed: A November ruling upheld a decision requiring Maryland and the federal government to consider Metro’s safety problems and declining ridership as part of their assessments for the Purple Line.

“We need to get on with this project,” Berliner said. “It’s important to Montgomery County, it’s important to Prince George’s County, it’s important to the state of Maryland.”

As for Metro, Berliner points out that more than a third of its riders are federal workers.

“The federal government cannot walk from its responsibilities to our Metro system,” he said.