SCOTLAND'S only reigning Commonwealth athletics champion, Yvonne Murray, has taken what she described as ''the hardest decision of my life'', in deciding she will not defend her 10,000 metres title in Kuala Lumpur this September.

The Motherwell athlete, who has raced only twice in the past sixth months, told team manager John Anderson yesterday. ''I have completely ruled out any event in Malaysia, and have indicated to the selectors that I will not be seeking selection,'' confirmed the 33-year-old Murray last night.

''Ever since I knew Kuala Lumpur was the venue, I have agonised over whether I should go. I can handle the heat, which is likely to be around 104 degrees, but I have a poor record in humid conditions. It is likely to be around 95%, and I just cannot cope with that.

''I am in training for the marathon, at which I see my future, and hope to make my debut in October.

''I am very patriotic, but this was a considered decision, rather than an emotional one. I would not want to go as defending champion and let Scotland down.

''I still want to be involved, and will gladly help with any fund- raising initiatives to help the team.''

Anderson, while appreciating her reasons, said he ''greatly regreted the loss of such an outstanding athlete and ambassador.''

Murray, who remains the most prolific holder of Scottish national and native track records indoors and out - 14 in all from 800 metres to 5000 metres in various age groups - insists this is not the end of her track career, though she acknowledges that major championships are now most unlikely.

Scotland's longest-serving internationalist, Murray made her Commonwealth debut in 1982, while still a pupil at Musselburgh Grammar School.

After moving to coach Tom Boyle, teaming up with Tom McKean, and backed by Ayrshire Mercedes dealer Glen Henderson, she achieved her most notable successes.

Murray's withdrawal is a devastating blow to Scotland's limited medal prospects in Kuala Lumpur, and follows Liz McColgan's decision to decline selection because of personal differences with the team manager. Between them, they have monopolised the 10,000m title for Scotland since the event was introduced to the women's programme in 1986.