Department deputy director-general Seree Jitsopha said the construction funding will be allocated in the 2015 budget.
The department is buying land for the airport. Currently, two owners have refused the prices offered for their land. Mr Seree said land expropriation could be an option if continue to refuse to sell.
The airport will have a 1.8 kilometre long runway, indicating that it will be used only for smaller aircraft. Phuket, for comparison, has a 3-kilometre runway and yet can still not handle takeoffs by fully-laden Boeing 747s or Airbus A380s.
Other airports also under consideration by the department would be in Surin and Amnat Charoen provinces in Isarn, and Satun in the south. However, the agency has not yet committed to building them. These three projects are still in the feasibility study stage, Mr Seree said.
Mr Seree added the site proposed for the airport in Surin is army land and too close to the town. The department would probably look for a new location if the plan goes ahead.
Satun has a small airport operated by the air force, and the one in Amnat Charoen belongs to the army. All four airports, including Betong, were proposed by residents and their MPs as commercial airports.
Building new airports requires approval from the National Economic and Social Development Board.