AN invitation arrived in the bulging Keeping Posted mailbag from Daliesque painter (in an artistic rather than physical sense) Phil Clarke to drink and dine at his Kennedy Road eyrie tonight on account of his 40th birthday. These are heady days for surrealist Clarke - sometimes referred to as a society painter because of the many socialites he has laid to canvas. Apart from his current exhibition at Pacific Place, he has a one-man show opening in Paris next month followed by another in Geneva. I will be at Clarke's black-tie shindig, if for no other reason than to ensure proper decorum is maintained (one can never be sure with these surrealists), and that the peace of the neighbours - many of whom are faithful Keeping Posted readers - is not disturbed. Incidentally, someone who refers to Clarke as ''a close friend'' (although I very much doubt it) whispered in my ear that when the artist celebrated his birthday last year, the cake had etched in icing sugar the distinct legend ''38 years''. ''So how come Phil is celebrating 40 years this time around?'' he asked rather pettily. Perhaps tonight at the party, Clarke will choose to explain this Great Leap Forward.