SCOTLAND'S golden eagle population is worrying conservationists, despite remaining relatively stable over the past decade.

While the latest population level of 431 pairs is actually a 2% increase since the early 1990s, this apparent good news masks declines in some mainland areas, raising fears that illegal persecution may be continuing on grouse moors and in sheep-farming areas.

In 1992, the estimated number of golden eagle pairs was 422. Scotland remains home to almost all of the UK's breeding population of golden eagles, with England gaining one breeding pair.

The figures announced yesterday were revealed in the most recent survey, conducted from January to July last year by the RSPB, Scottish Natural Heritage and the Scottish Raptor Study Groups.

There are also fears that the apparent increase in numbers of 2% could be because of a more comprehensive survey for this latest study.

The groups involved were delighted at the 147 pairs recorded in the Hebrides - an increase of 23 - but warned about figures on the mainland.

South of the Great Glen, the figure fell from 140 in 1992 to 127 last year, a decrease of 9.3%. North of the Great Glen the fall was much smaller, from 158 to 157.

A report last year found that although golden eagles are officially protected, a disproportionate number of dead birds were recovered from sporting estates where they still appear to be subject to persecution by poisoning, although landowners and gamekeepers deny this.

Eagles are also still thought to be persecuted in some sheep-farming areas. Afforestation, deterioration of the habitat and disturbance by egg collectors present other dangers.

Dr Helen Riley, secretary of the Scottish Raptor Monitoring Group and an ornithologist with SNH, said they were delighted with the increases in particular areas, but warned: ''The overall decline reported from the Scottish mainland, however, is very disappointing and needs to be investigated to see whether the predictions that this is caused by ongoing persecution are confirmed.''

She added that, in the Western Isles, ''we have reports that persecution in many areas has now stopped, which must be a big factor for the success there. Habitat and availability of prey will be other factors.''

Patrick Stirling-Aird, of the raptor study groups, said: ''While at first glance the picture for golden eagles in Scotland seems healthy, there is real cause for concern over the population decreases in eastern areas of the Highlands and over poor breeding success in some locations there.

''The underlying causes of such population decreases and low breeding success need to be tackled to help bring the Scottish golden eagle population up to a more satisfactory natural level.''

Dr Jerry Wilson, head of research for RSPB Scotland, said further investigation was needed to find the reasons for the decline on the mainland.

''Although numbers appear to have held up well overall since the last survey 11 years ago, there are encouraging increases in some areas and worrying declines in others. Analyses of the survey results will give us a clearer picture of the likely causes of these differences.''