BOSTON - Long-delayed repairs to Groveland Bridge, which connects Haverhill and Groveland, would be completed within the next three years under a plan floated yesterday by state Treasurer Timothy Cahill.

He is proposing that the state borrow against future federal highway funds to get money now to pay for repairs to 10 bridges among 500 in the state that were cited as "structurally deficient" in a report released during the summer by the Patrick administration.

The bridges, which also include the John Greenleaf Whittier Bridge between Amesbury and Newburyport, have not been maintained because the state hasn't identified a way to pay for the work.

The Whittier Bridge on Interstate 95 spans the Merrimack River and is crossed more than 75,000 times a day. In August, state officials said the 53-year-old bridge is safe but is considered to be "functionally obsolete."

The 101-year-old Groveland Bridge is crossed more than 21,000 times a day.

"It's an opportunity to leverage what the federal government is giving us," Cahill said yesterday. "It's a win-win situation."

The combined price tag for repairing or replacing the 10 most expensive bridges is $690 million. Of that, the Whittier Bridge repairs would cost $132 million and the Groveland Bridge would cost $75 million, according to Cahill's office.

Under the plan, Cahill would have the state borrow $600 million by issuing tax-exempt municipal bonds. The state would pay the rest out of its own funds.

The state would repay the bond holders through federal highway money it would receive in future years. Cahill would borrow all of the money over three years, and not borrow more than 20 percent to 30 percent of federal highway money due the state between 2015 and 2021. The state would begin repaying bond holders in 2015, after the Big Dig debt has been paid off.

The Big Dig's $15 billion cost led to many of the bridges' repairs being delayed. Cahill warned the state should act now to come up with the money for the repairs rather than waiting until after the Big Dig has been paid for in 2015. Waiting would make the projects more expensive, and the cost could reach $1 billion. By borrowing now when interest rates are falling and construction costs haven't risen, Cahill said the state could save hundreds of millions of dollars.

While saving money is his angle, Cahill said the motive for pitching the borrowing plan is public safety.

"If we wait to 2015 to address these bridges, there's a good chance one of them will be closed at that point or even worse," Cahill said. "But they'll be guaranteed they'll cost a lot more money."

In August, the Patrick administration reported that more than 500 of the state's 4,500 bridges were structurally deficient, meaning they were safe but needed to be repaired.

The Transportation Finance Commission last year reported that the Big Dig is responsible for Massachusetts having $20 billion in unmet road and bridge maintenance.

Any borrowing needs to be approved by the Legislature and the Patrick administration.

Sen. Steven Baddour, co-chairman of the Legislature's Transportation Committee, credited Cahill with trying to tackle a difficult problem.

"I'm glad that people other than traditional transportation folks are talking about transportation," said Baddour, a Methuen Democrat.

Baddour, who hadn't seen the details of Cahill's plan, said he wasn't ready to pass judgment on it, although he said he preferred it to the Transportation Finance Commission's major recommendation for paying for transit repairs.

"If it pushes off raising the gas tax, it's a good thing," Baddour said.