ST. PAUL — In a sudden shift Friday, the Minnesota Senate revived the possibility of raising the gas tax for roadwork and a metropolitan area sales tax for mass transit projects by making over what had been a stand-pat transportation finance plan.

The revision came in a surprise amendment that would raise the gas tax by 5 cents over four years and impose an extra half-cent sales tax in the Twin Cities area over the same time span.

The two taxes would raise about $1 billion combined, money that supporters say are needed to handle a backlog of road and bridge work around the state and expand transit options.

“Failing to fund transportation doesn’t make the problem go away, it just keeps getting more expensive,” said freshman Sen. Melissa Franzen, DFL-Edina. “This is how we pay for things.”

The change embraced by Democratic caucus leadership was adopted on a 34-26 vote. The bill itself passed on a 35-27 vote. No Republicans voted in favor of the amendment or the underlying bill.

Legislative Democrats had retreated from a gas tax increase after Democratic Gov. Mark Dayton publicly balked at it. His spokesman, Bob Hume, said Friday evening that the governor has not changed his stance in opposition to a gas tax increase. He has urged transportation advocates to regroup and make another push in the 2014 session.

Dayton does support the sales tax, which would be assessed in the Senate bill at the rate of a quarter-percent the next two years and another quarter-percent the following two years.

Republicans cried foul over what they saw as a backroom deal sprung on them.

“This is tax policy hokey-pokey,” said Sen. David Osmek, R-Mound.

The House has passed a transportation plan without any tax increases. The Senate version now heads back the House, which can choose to adopt it or send it to a conference committee.

Senate Transportation Committee Chairman Scott Dibble, DFL-Minneapolis, said the fallback option is a “lights on” bill that merely keeps the state transportation department open and crews working on previously authorized projects. He’s holding out hope of a late breakthrough.

“We’re putting together a transportation bill that we think on principle and policy is what we have to do,” Dibble said.