Massachusetts transportation officials Thursday backed a $1.8 billion budget for the MBTA that calls for a substantial increase in state funding to bridge a yawning deficit and avoid steep fare hikes.

The debt-ridden agency faces a $139 million shortfall for the next fiscal year.

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“We cannot afford what we have,” Beverly Scott, general manager of the Massachusetts Bay Transportation Authority said at a finance board meeting. “It is a structural problem. The time is now. It must have a structural fix.”

Governor Deval Patrick has proposed increased funding for public transportation through tax hikes. Board members expressed optimism lawmakers would approve the plan.

Officials outlined $21 million in budget cuts and $118 million in additional state funding to balance the budget. The plan now goes to the full state transportation board early next month.

Jonathan Davis, the MBTA’s deputy general manager, said that without new state funding the system would have to take a number of steps, including raising fares by an average of 19 percent, a hike that would raise an estimated $39 million.

Without new state aid, “we will take steps immediately after July 1 to close that gap.” Fare hikes would go into effect around December. Under the plan, subway fares would rise from $2 to $2.45, while bus fares would climb from $1.50 to $1.85.

Under the plan, the cost of The Ride, a curb-to-curb service for passengers with disabilities, would remain unchanged at $4.

Last year, the MBTA raised fares 23 percent to balance its budget. The agency has battled financial difficulties for years and is burdened with heavy debt. Of the $1.8 billion budget, $443 million goes to debt payments.

The MBTA is the most “highly leveraged transportation service in the country,” Davis said.