At the urging of St. Paul and Ramsey County officials, Metro Transit will grudgingly back off immediate plans to pursue a $28 million rapid bus line from downtown St. Paul to the Minneapolis-St. Paul International Airport and the Mall of America.

The regional transportation agency had previously announced that the B Line — a limited-stop, “arterial” bus rapid transit (BRT) route — would roll into place by late 2016, one of about a dozen rapid bus routes in the works over the next 12 years.

Metro Transit officials said the decision to delay that proposal puts more than $18 million in promised federal funding in jeopardy.

“The delayed design project will not meet funding sunsets, and the B Line project will lose $18.6 million of secured funding,” said Charles Carlson, a senior manager of BRT projects with Metro Transit, in a memo to the Metropolitan Council on Wednesday.

It might be possible, however, to move those funds to a different corridor.

Concerns about three overlapping city, county and Met Council efforts to launch a new transit line on West Seventh Street have been quietly bubbling over the past year.

St. Paul City Council Member Dave Thune, who represents West Seventh Street and sits on the Riverview Corridor policy advisory committee, said it would be unfortunate to begin building stations and sidewalk bump-outs for one mode of public transit, only to have to replace them for another.

“We can’t have all these processes going on at once and expect a comprehensive solution,” Thune said.

In meetings with Metro Transit, county officials have expressed concern that the three visions could compete for local and federal funding.

City and county officials say they plan to spend the next 12 to 18 months studying the Riverview Corridor, a possible transit link from the Union Depot on Kellogg Boulevard to the airport. They said it’s unclear whether the corridor would be served by streetcars, rapid buses or a combination of the two, and Metro Transit’s overlapping plans muddy the issue.

The Met Council’s transportation advisory board voted last week to put the expedited process for the B Line on hold. Ramsey County Commissioner Mary Jo McGuire made the motion, which was seconded by St. Paul City Council member Chris Tolbert, who represents part of the route through Highland Park.

“Wait until after the Riverview Corridor study is done, rather than having multiple studies going on at the same time,” said Tolbert, who serves as an alternate to council member Russ Stark on the advisory board.

The motion passed unanimously, and the 17 members of the Met Council were briefed on the decision Wednesday.

The advisory board’s decision does not interfere with Metro Transit’s plans to launch an arterial BRT line along Snelling Avenue and Ford Parkway next year.

The St. Paul City Council recently voted 6-0 to study a potential streetcar route along four miles of Seventh Street, from Arcade Street to Randolph Avenue. Before the vote, Tolbert amended the council resolution to ensure that the Riverview Corridor study moves forward first.

County officials see the Riverview Corridor as the missing leg of a transit triangle. Metro Transit’s Hiawatha Line, which debuted in 2004, connects the airport to downtown Minneapolis, and the new Green Line connects downtown Minneapolis to the Union Depot in downtown St. Paul.

Ramsey County, the lead agency studying the Riverview Corridor, is working with the city, the Minnesota Department of Transportation, the St. Paul Area Chamber of Commerce, the Met Council, Metro Transit and other agencies, said Sara Thatcher, a county spokeswoman, in an email.

“The study will cover all modes of transportation, including streetcars,” Thatcher said.

The price of the study is slightly less than $1.5 million.

Frederick Melo can be reached at 651-228-2172. Follow him at twitter.com/FrederickMelo.