PORTLAND – When the first Amtrak trains from Boston roll into town in December, a new interterminal shuttle bus service will connect the region’s transportation centers.

The shuttle bus service will link the Amtrak station and adjacent Concord Trailways bus station at Thompson’s Point with the Casco Bay Ferry Lines terminal in downtown Portland, the Portland International Jetport and several hotels.

The Greater Portland Council of Governments asked area bus operators Wednesday to submit proposals to run the new service starting Dec. 15, the day the trains arrive.

“I think there is a desire for some public transportation to alleviate congestion, and there are parking issues at the jetport,” said Jeff Monroe, Portland’s transportation director. “It’s a next step working toward an interterminal transportation system.”

Monroe long has talked about creating a seamless connection among various forms of transportation for people coming to Portland, or those using the city to connect with other destinations in Maine.

The combined train-bus station at Thompson’s Point is being dubbed the Portland Transportation Center.

The shuttle will provide express service between the various stops and will have room for baggage.