Weighing rising costs and political opposition, planners of a light-rail line between Minneapolis and the southwest suburbs are focusing special attention on three options for resolving a conflict between the future LRT route and existing freight train traffic.

They are exploring details on burying the LRT lines in a deep or shallow tunnel beneath the freight traffic in the Kenilworth corridor of Minneapolis, and scrutinizing a plan for rerouting freight trains to St. Louis Park.

Those are among eight options under consideration by the Metropolitan Council, the agency building the Southwest Corridor LRT. The agency this week revealed that solving the freight train problem could increase the cost of the $1.25 billion project by $120 million to $420 million.

“The Metropolitan Council has given no direction to approve or disapprove any of the eight options,” agency spokeswoman Laura Baenen said Friday. But she added that the agency is “focusing on three options … and working with the cities to refine those three designs.”

In Minneapolis, Mayor R.T. Rybak’s aide on transportation, several City Council members and public works officials met this week with staff members of the Met Council to discuss details of the two tunnel options.

While the city has endorsed putting the LRT in Kenilworth over the ­objections of some residents, it has long insisted that the freight traffic be relocated rather than running along the future light-rail line and existing bike and running trails.

“We’re willing to look at tunnel options to keep the project going,” said Peter Wagenius, Rybak’s transportation adviser.

But Wagenius said the mayor is uneasy about embracing a deep tunnel out of fear that its high cost will doom it and the city will end up with the LRT, freight and recreational trails at ground level. At $420 million, the deep tunnel is the most expensive option.

The shallow tunnel would add perhaps $250 million to the Southwest LRT cost. Met Council Chair Susan Haigh called the shallow tunnel “one of the most promising” options Friday in a call-in show on Minnesota Public Radio.

“It is a more promising option than we initially believed before seeing the cost estimates,” Haigh said, adding that agency staff is trying to find ways to further trim the cost of a shallow tunnel.

Haigh stressed that she was “absolutely not” committing herself to a shallow tunnel.

A shallow tunnel also poses problems. It would be interrupted north and south of a channel between Cedar Lake and Lake of the Isles, where the LRT lines would run above ground and water. A shallow tunnel would be dug as a trench and could cause more disruption and damage than a deep tunnel, Wagenius said.

The Met Council also has talked in detail recently with St. Louis Park city officials about a plan that would route freight on berms as high as two stories just south of the St. Louis Park High School football field and add up to $290 million to the cost of the LRT project.

The Met Council is concentrating on that reroute plan, which would involve acquiring 32 homes, businesses and other property, rather than a plan that called for running the freight traffic through the football field.