WASHINGTON — More than a decade ago, Hurricane Katrina washed away many of the railroad tracks that line the Gulf Coast, leaving the region without a regular route to carry passengers.

Now, Amtrak is trying to restore service in the area, but the effort has stalled after bitter clashes with freight rail companies, which control most of the tracks the agency uses outside the Northeast. At the heart of the rancor is the meaning of a law governing which side has priority over use of the tracks and when, a longstanding battle that has spilled into the courts and onto social media. The outcome, experts say, has broader implications for Amtrak’s future.

The conflict underscores a persistent challenge for Amtrak. Although the infrastructure deal the Biden administration reached with a bipartisan group of senators last week would help fulfill the agency’s elusive goal of expanding across the nation, one of the biggest obstacles would be negotiating with […]