The expansion also would upgrade living quarters for on-duty firefighters, said Cecil Bittinger, company president.
Cochrane said the expansion could cost $150,000 to $200,000, but fire officials haven't gotten formal estimates yet.
The fire company, which owns the building, would pay for the expansion, Bittinger said.
When the work would be done isn't certain. Fire company officials must apply to the Board of Zoning Appeals for permission to expand, since the building is in a residential area, Cochrane said.
If the company adds two bays, the fourth bay would provide room for a new fire engine the company hopes to get in three years, Cochrane said.
The third bay would house a Mack fire engine that Antietam Fire Company is using because that company's fire engine is being repaired, Cochrane said.
The fire hall was started in 1932 and two engine rooms were added in 1949, Bittinger said.