The government's conservation watchdog has been accused of putting wildlife and wild places at risk by preparing to relax its defences against development.

Scottish Natural Heritage (SNH) is under fire from environmental groups and insiders for allowing plans for a coal mine and wind farms to go ahead, despite the damage they could do to rare birds and peat bogs.

Critics warn that a review of corporate strategy being led by SNH chairman Andrew Thin could result in more damaging developments being given the go-ahead. Fears have been fuelled by a recent interview in which Thin said he was neither a conservationist nor an environmentalist.

Thin, whose background is in economic development, is attempting to re-orientate SNH to be more in line with the SNP government's priorities for sustainable growth. He aims to win backing from ministers, who have previously said they intend to merge SNH with the Scottish Environment Protection Agency.

But Thin's approach has caused consternation among some of his staff - who are anxious that their primary responsibility to protect nature is being eroded - and has provoked strong criticism from RSPB Scotland.

The society's director, Stuart Housden, said: "We are aware SNH is presently reviewing its approach to planning applications and are concerned that recent decisions suggest the outcome of this review could result in a dilution of protection currently afforded to Scotland's natural heritage."

RSPB Scotland's concern has been sparked by a case in East Ayrshire in which SNH is planning to allow an open-cast coal mine to be extended into a protected area important for bird life and blanket peat bog. SNH has blocked plans to expand the mine three times, but a new application looks likely to win planning approval within the next 10 days.

Although SNH has formally objected to the latest proposal for the Grievehill mine in New Cumnock, it has indicated that the scheme could go ahead as long as certain conditions are met. It has accepted that 18 hectares of peat bog will be lost, but pointed out that it had a "balancing duty" to take account of the social and economic benefits.

But RSPB Scotland argued that, by permitting the expansion, SNH had failed the first test of any agency charged with protecting wildlife.

SNH has also been criticised by local environmental group Mining and Environment Group Ayrshire (Mega). "We are becoming increasingly concerned that SNH, our supposed environmental guardian, is tempering its objections to the many extensions to open-casting we are experiencing here in East Ayrshire," said its secretary, Greta Roberts.

SNH defended its stance, insisting that Grievehill did not create "a significant precedent". Its director of operations in southern Scotland, John Thomson, accepted a bit of bog was being "sacrificed", but pointed out it was only 0.17% of the protected area.

RSPB Scotland highlighted two other recent cases in which SNH's approach had sparked alarm. SNH did not object to a wind farm in Corriegarth, near Inverness, despite evidence that it would kill golden eagles, and it withdrew an objection to a wind farm at Fairburn near Dingwall, rejecting advice that it could harm red kite populations.

But Thin dismissed the suggestion that SNH was weakening its protection of wildlife areas. "We are treating these cases in the same way as we have always treated them," he told the Sunday Herald.

"What we are trying to do is to spell out why Scotland's natural heritage is important to all Scottish people. Some people have interpreted that as losing focus on the environment, but the organisation is just as passionate about that as it ever was, and I am just as passionate about it as I ever was."

In a recent article in SNH's internal newsletter, Thin upbraided staff who criticised his strategy review. He wrote: "The idea that there may be a contradiction or even a conflict between caring for our natural heritage and increasing its relevance to the everyday needs of the Scottish people must surely be fundamentally flawed."