Campaigners who want 371 sq km of land in West Sussex and Hampshire reinstated into the proposed South Downs National Park are meeting to discuss the scheme.
The proposed national park runs from Eastbourne to Winchester
Sir Martin Doughty, chair of Natural England, is in the Western Weald to talk to the chairman of Midhurst Town Council to hear local views.
Natural England believes the Western Weald could be vulnerable to development if it is not included.
A public inquiry into the national park reopens on 12 February in Worthing.
The South Downs is the only one of 12 areas originally recommended 60 years ago by the National Park Committee which still does not have the status.
It was designated as a national park in 2002, followed by a two-year public inquiry.
The boundaries of the proposed park were re-drawn this year, leaving out Liss and Petersfield in Hampshire, and Midhurst and Petworth in West Sussex.
The government decided to exclude the Western Weald because its sandstone geology differs from the majority of the park's chalk downs.
"The grounds for excluding the Western Weald are not consistent with already designated national parks such as the Peak District and Lake District which contain more than one landscape character," said Sir Martin.
"Natural England believes the smaller boundary is the wrong decision and it is high time we awarded the South Downs the elite national park status it deserves."
If it is not included in the national park, the Western Weald could lose the protection it currently receives as an area of outstanding natural beauty.
Natural England is encouraging supporters of the Western Weald to speak for its inclusion at the national park public inquiry.