Maine’s three metro areas are expected to grow slowly this year and next, a forecast prepared for the U.S. Conference of Mayors said.

The report, released Thursday, said metropolitan areas contribute the lion’s share of economic growth, jobs and wages in the U.S.

That’s true in Maine as well: The report said the Portland-South Portland-Biddeford metro area accounts for 50.5 percent of the statewide economy and Bangor contributes another 10.3 percent, followed by Lewiston-Auburn, with 7.5 percent of the state’s economy.

Portland’s economy will grow by 1.2 percent this year and 2.1 percent next year, from $28.6 billion to $29.8 billion, the report projected. That compares to average growth in all metro areas of 1.9 percent in 2016 and 2.7 percent next year, the report said.

Bangor’s economy is expected to grow by 0.6 percent this year and 1.6 percent next year, the forecast said, while Lewiston-Auburn’s output of goods and services is expected to grow by 1.8 percent this year and 2.0 percent in 2017.

The economies in all three metro areas contracted in 2012-14, the report said, with Portland-South Portland’s shrinking by 0.6 percent and Bangor and Lewiston-Auburn’s economies both contracting by 1.3 percent. Portland’s economy grew by just 0.4 percent last year, the report said, while Bangor’s contracted another 0.3 percent and Lewiston-Auburn’s grew 0.2 percent in 2015.

Amanda Rector, the state economist, said the projections are “not surprising,” because of the state’s aging population and recent slow growth statewide.

She also said comparisons of Maine’s small metro areas to larger metro areas are difficult.

“Given that many of the large metro areas around the country have been seeing tremendous growth, it’s hard to compare to the national average,” she said. Rector said the state needs to develop policies that foster economic growth and encourage younger workers to move to the state to create more sustainable growth.

Charles Lawton – who writes a weekly column for the Portland Press Herald – an economist with Planning Decisions, a research and planning firm, agreed that the forecast falls in line with what most economists would expect to see.

He said without some massive shift in the national economy, there’s not much expectation that Maine metro areas will suddenly shoot up in output compared with larger, more robust economies in areas such as New York City or Silicon Valley.

Lawton also said the fact that metro economies account for two-thirds of Maine’s output is also not shocking, especially since the manufacturing base in rural areas has been in decline for years.

“Every time a paper mill in Lincoln or Baileyville shuts down, the remaining economy shifts to more of a consumer economy,” he said. And the consumer economy in Maine, where the population is the oldest in the country, isn’t very robust, with much of the spending by people on fixed incomes with high health care costs.

“This simply reinforces the need to attract more, younger workers” to the state, Lawton said.