PORTLAND – The Federal Railroad Administration has reasserted its position that the Boston-to-Portland passenger rail service can safely run at 79 mph.

The decision, announced Thursday, supports the positions of the Maine Transportation Department and the Northern New England Passenger Rail Authority that the 115-pound rails between Plaistow, N.H., and Portland are safe for speeds higher than the 59 mph advocated by the track’s owner, Guilford Transportation.

The federal Surface Transportation Board is to decide on the matter by the end of the month.

The long-awaited Amtrak service now is scheduled to begin this fall.