THE northern Sydney home of the largest owl species in the country is about to become home to something much larger.

The state government has introduced legislation to elevate more than 3800 hectares of the Berowra Valley to national park status. And it is not only the powerful boobook owl that is hooting with delight.

Environmentalists have been campaigning for the Berowra Valley Regional Park in the Hornsby shire to receive national park recognition for nearly six decades.

Bob Salt, the Friends of Berowra Valley Regional Park chairman, said the society would not rest until the legislation had passed through Parliament.

''We've been writing to local members, we've made approaches to conservation councils, we've held exhibitions and we've created a guidebook,'' Mr Salt said. ''We are very pleased about this attempt to give it national park status.''

He said the move would make nature conservation, rather than recreational activities, the focus of the park's management.

But the Environment Minister, Robyn Parker, said public use of the valley would not be compromised, with well-used dog-walking tracks excluded from the legislation and the possible introduction of mountain-bike tracks.

The Hornsby Shire Historical Society museum co-ordinator, Elizabeth Roberts, said the valley provided a link to Australia's colonial and indigenous past.

The park has dozens of historically significant areas, including Aboriginal artwork and campfire sites. It also has the Thornleigh Zig Zag Railway, built in the late 19th century and the last of its kind in the state.