They say the 1200-membership club is struggling with an uncertain future, losing $200,000 a year and on a dodgy mission to degrade some of Australia's most valuable box gum woodlands.

The club has engaged Sydney developer MBark, which has built retirement villages at Camden and Berry, and says its latest proposal is in its infancy, while opponents say 70 to 80 three-bedroom villas for over-55s will be built on a disused fairway east of the 14th fairway. A club briefing note says:"The land above the 14th hole lends itself to magnificent views of the Brindabellas and the golf course."

Stage two will be 70 two-bedroom apartments near the club house. Between 120 and 150 dwellings overall will be built.

Red Hill Regenerators conservation officer Dr Michael Mulvaney says this was the seventh attempt at developing the fringe of Red Hill Nature Reserve: "When is a no a no?" he said. "How can they be allowed to keep picking open a scab?"

Federal Golf Club vice-president Bob Correll says the club was not losing $200,000 annually, it was paying off loans, and the longer term issue was new infrastructure including replacing a 30-year-old irrigation system.

"Operationally the club is sound, one year there is a modest loss, one year a profit, but right now what it needs most is a substantial capital injection," Mr Correll said.

Experts say Red Hill was once part of a yellow box woodland extending north to Toowoomba and south to Melbourne, until 95 per cent was cleared. Patches left are generally less than five hectares. Red Hill is 375 hectares, the second largest patch anywhere in Australia, which makes it more valuable for breeding habitat.

Bulldozers would take down 300 native trees, many with old nesting hollows. Dr Mulvaney says new housing would bring cats, dogs, weeds, European wasps, and Indian mynas in, driving out rare birds like the scarlett robin and painted button quail, outraging people. "We are not going to be alone [fighting proposal] , there will be the Conservation Council, the Canberra Ornithologists group, Friends of Grassland, National Parks Association, residents association."

The regenerators group's president, Ross Kingsland, said although every previous proposal had been rejected, he was wary of the ACT's drive for infill and housing. "One of my big concerns, this is the first, there are other spots within the golf course that they see are suitable for developing, they only need to hit another financial bump?"

The group says an aged community would be established in a fire-prone area, isolated from services, shops and public transport, and dependent on cars on roads that were already busy.

"It is little wonder that authorities have repeatedly labelled past proposals as poor planning and unsupportable," Mr Kingsland said. The regenerators hope golf club members would see the folly, waste of scarce resources and community angst that resurrection of rejected proposals would cause.

Mr Correll said the Council of Aging said the need for over-55s accommodation in Canberra was significant. The club had listened carefully to the regenerators group, and was aware the group was against any sort of development. The club was confident MBark's development would enhance the environment with walking trails.