A battle is looming in the depths below downtown Los Angeles as transportation planners try to find a way to smooth out the commute for thousands who take rail into the city center each day.

The Los Angeles County Metropolitan Transportation Authority is studying how to link the three major rail corridors that go into the city center: the Blue Line, the Gold Line and the upcoming Exposition Line.

The idea is to create a rail thoroughfare so that passengers can travel seamlessly from Pasadena to Long Beach -- and eventually from Culver City to East L.A.

There is widespread agreement that linking the rail lines would help commuters, who must switch trains at least once to get through downtown. But some downtown residents worry that part of the rail connection would be above ground, potentially clogging already crowded streets."It would be a pox for the neighborhood," said Eric Richardson, a member of the Downtown Neighborhood Council and the editor of www.blogdowntown.com.

Richardson and others want a commitment from the MTA that all rail connections would be underground, which could hike the price of the project.

At two public meetings this week, the MTA is to unveil potential routes through downtown that would fill in the 1.6-mile gap between Union Station and the 7th Street/Metro Center station. Dolores Roybal Saltarelli, transportation planning manager for the MTA, said the routes and potential stops were being determined in large part by input from public meetings held last year.