Heathrow airport operator BAA told the London Assembly it could not rule out the need for more "capacity" beyond its current expansion proposals.
Critics say communities will suffer from increased noise levels.
The assembly's environment committee met to consider the environmental impact of a proposed plan to include a third runway and a sixth terminal.
The plan would require Sipson village to be bulldozed and 50 communities and towns could suffer increased noise.
Local councils, campaigners and industry leaders attended the meeting.
The committee is expected to send its recommendations on the current proposals to the government on 26 February.
'Hostage to fortune'
Chief executive of BAA, Stephen Nelson, said that unlike his predecessor, who ruled out expansion in 1994, he would not commit to anything.
"It is very important for me to emphasise looking forward. I will not be giving undertakings which, in some sense, could be considered hostage to fortune in the future.
"It would be inappropriate for me to speculate on whether there will be a further case for capacity expansion beyond 2030."
Those opposing the plan said the public consultation process was unclear, too technical and has not been able to reach all those who might be affected by the proposed flight paths.
Members of Hacan Clearskies and Future Heathrow pressure groups presented their opinions for and against the expansion.
Members of the 2M Group, which represents 12 local authorities who expect to be affected by expansion of Heathrow Airport, were also at the meeting.
The plan would have an impact on the London boroughs of Ealing, Hammersmith and Fulham and the boroughs of Slough, Windsor and Maidenhead, Spelthorne and South Bucks District Council.
Darren Johnson, chairman of the Environment Committee said: "Now we hear that even more expansion beyond the current proposals cannot be ruled out.
"We have heard the economic benefits of Heathrow are overestimated, while the costs of expansion, in terms of increased carbon emissions and the detrimental impact on peoples' quality of life, may have been underestimated."
BAA has argued a third runway could be worth £9bn a year to the national economy but the government has said any expansion must comply with EU limits on noise and air pollution.