The two males were spotted at about 10.30am allegedly setting fire to grass behind the Southland Shops in Mawson, close to a petrol station and several other businesses.

The fire was quickly extinguished by the ACT Fire Brigade and the offenders, aged 14 and 15, were arrested on the scene.

The blaze was contained to about 50m, according to police.

South district acting Superintendent Bob Wynn said police were still considering whether to charge the youths.

''This is something that police will not tolerate, and we will act swiftly, utilising a full range of resources and legislative options, to identify and deal with any people responsible for such an act,'' he said.

''We are obviously aware of the public opinion of what's going on, particularly in Victoria, but also in NSW, and we've also got the memory of the January 2003 bushfires here in Canberra.

''But each situation has to be judged on its own merits, so we obviously have to be careful about what course of action we take.''

In an unrelated incident, a man returned to his Cowder Circuit home in Stirling early yesterday morning to find a small fire alight on his doorstep.

The 18-year-old threw water on the blaze before any damage could be done. Police are investigating the incident.