The proposed national park covers parts of Sussex and Hampshire
Calls for the creation of a South Downs National Park have come from campaigners on the 60th anniversary of legislation to protect rural areas.
The Campaign to Protect Rural England (CPRE) said top priority should be given to beautiful landscapes.
The South Downs area, covering parts of Sussex and Hampshire, is the only one of 12 national parks proposed in 1947 which has not since been created.
Legislation to create national parks went before parliament in 1949.
A decision on the planned national park, which was the subject of a public inquiry after changes to the boundaries were proposed, could be made this week.
Tom Oliver, head of rural policy for the CPRE, said the creation of national parks came at a time of huge challenges to society following World War II.
He said: "As we face future challenges of a similar scale and unprecedented pressures on our land and natural resources, government should again give top priority to beautiful landscapes and the qualities and opportunities they offer us all."
The CPRE wants further protection for vulnerable areas such as the Forest of Dean and the English border with Wales.
The campaign group has also called for extensions to existing national parks such as the Lake District and Yorkshire Dales.
It has raised concerns that England's best landscapes are threatened by developments such as wind tubrines, electricity pylons and a lack of investment in hill farming which helps preserve the countryside.