Haven House Visitor Centre at Titchfield Haven Nature Reserve is now an 'Asset of Community Value'.
Hampshire County Council, which owns most of the site, recently proposed to sell Haven House and Haven Cottage.
Facilities like the Titchfield Haven Visitor Centre, cafe, meeting room, toilets, as well as office space and a ticket sales point are based in Haven House.
The application to make the visitor centre and cafe an ACV - approved by Fareham Borough Council - was put forward by Hill Head Residents’ Association.
It means that the centre and cafe will remain on the ACV register for up to five years, so if the County Council goes ahead with its plans to sell during this time, it must notify Fareham Borough Council.
The Residents’ Association will then be given up to six months to prepare a bid to buy the site, which cannot be sold to anyone else in the meantime.
The application was approved given that the site is an important community hub, used by more than 85,000 visitors per year.
Executive Leader of Fareham Borough Council, Cllr Seán Woodward, said: "I am very pleased that Haven House has met the criteria to be deemed an Asset of Community Value.
"This is an incredibly well attended venue with a popular cafe for local residents as well as walkers, cyclists, surfers and swimmers alike. The Visitor Centre showcases art and craftwork from local talent and also holds community events throughout the year.
"Haven House is a perfect candidate to be registered as an ACV and I hope this decision goes some way to protect the venue long into the future."