The move came after trust chairman William Proby warned of the threat to open countryside at the body's AGM last week.
The trust, one of the UK's largest landowners, is concerned that rural areas are increasingly at risk of development due to the government's house building drive.
Policy director Tony Burton said an appeal for funds is being considered to buy up land and stop development. This could be similar to the trust's Neptune campaign, which has raised £45 million and enabled it to buy 665km of coastline. It is also looking at acquiring development rights through covenants.
Burton added that the trust may become more involved in planning inquiries even where it has no direct interest in a site.
"We could contribute selectively where there are issues of national precedence," he said. He argued that plans for eco-towns and growth areas could undermine the good work done on driving brownfield development.
The trust is consulting members and the public on the issue before deciding what action to take.
The Federation of Master Builders backed the trust, suggesting that existing settlements have the potential to offer the homes needed.
But a DCLG spokesman said the trust's claims "misunderstand the planning protections that are in place to safeguard the countryside".