LOS ANGELES_They call it the "subway to the sea," although so far it exists only on paper.

For years, transit planners dreamed of a subterranean train along Wilshire Boulevard from the skyscrapers of downtown to the beaches of Santa Monica, a 15-mile line that could free at least some commuters from the inevitable freeway gridlock.

The ambitious idea died years ago, leaving a stunted line that dead-ends just a few miles from downtown. But as streets and highways grow increasingly clotted, there is renewed talk of completing it.

The proposed line, envisioned decades ago by then-Mayor Tom Bradley and now embraced by Mayor Antonio Villaraigosa, would cut through an area with the region's densest concentration of jobs and people.

It's the most obvious route for a subway in the country and would be crowded from the day it opened, said Brian Taylor, director of the Institute of Transportation Studies at the University of California, Los Angeles.

"If you were going to build rail, the first place you would build it is down Wilshire," he said.

The project is getting another look following an about-face by Rep. Henry Waxman, a former opponent who pushed through a 1986 federal prohibition on tunneling through the area.

At the time, he feared construction could cause an explosion of naturally occurring methane gas. But new research has convinced the Los Angeles Democrat that tunneling can be done safely and he has introduced legislation to lift the ban.