ANYONE with a memory stretching hack more than 10 years will be able to recall that until recently, women who worked in offices usually occupied at best clerical positions - and dressed accordingly. But that scenario has changed enormously and so too have the rules of clothing.

They've had to do so because the number of professional women in Ireland has been registering a steady increase. According to the Central Statistics Office, while there were 101,400 females in the main professional services in 1985, a decade later that figure had grown to 140,700. Last year the Law Society had approximately 20 per cent more women coming onto its rolls than men, while the Institute of Chartered Accountants has seen its female membership grow from 7.6 per cent of the total to 17.63 per cent between 1985 and 1995.

Now frequently occupying roles always assigned to men in the past, women have evolved their own dress code which, while acknowledging traditional male forms, still has its own distinct style.

To begin with, female office clothing doesn't have to be excessively masculine in cut or form. "Absolutely not," insists Mary Finan, president of the Dublin Chamber of Commerce. "I don't think we have to ape men or look unfeminine. Anyway, it's not a male/ female thing; it's more dressing properly for the occasion. I certainly don't think you have to look like a man."

What's needed are clothes which give a clear sense of the wearer's professional abilities and that is why men have developed a strong dress code for the office. "It's very clear when you look at male clothing," comments Irish Life Assurance's chief executive Jean Wood, "that there are powerful constraints at work. As women have moved into more powerful positions, we've had to renounce some freedom. Inevitably, in that process our clothes have taken on more aspects of a uniform because uniforms tend to condition your responses".

Central to this uniform is the jacket, an item of clothing which has become the single most important part of the working woman's wardrobe. So Jean Wood says she would usually wear a jacket, with the proviso, of course, that "it's not a female version of the male suit".

Similarly, Rose Callan, a foreign exchange dealer with Citibank, would always wear a jacket. "You have to look smart all the time," is how she explains this decision. "You want to look businesslike, conservative."

That, it seems, is the message conveyed with jackets; that the woman wearing the garment is a professional among her peers. "I'd never come to work without a jacket," insists Barbara Patton, head of marketing at Irish Permanent. "Without it, you're not dressed for work." Like many women, Ms Patton has worked out her own dress code for the office environment and this bears little resemblance to what is worn at other times. Jackets suggest work, as do suits, another staple of the female professional who, in this instance, is following the example of her male colleagues.

Unlike them, however, she has greater freedom over both form and colour. There appear to be no absolutes when it comes to choosing between trousers and a skirt for suits. "I gather when I first started wearing trouser suits it was a change here," remarks Barbara Patton, "but no one said anything about it. If anything, I think with a trouser suit you have to look even more formal."

Although she never wears trousers herself Mary Finan agrees with this opinion, while Jean Wood, as an occasional trouser wearer, "wouldn't see any constraint against them". As for skirts, she says "a wide variation's acceptable except they can't be too short. In any case, most women in senior positions would be older, so they wouldn't want to wear anything very short."

Rose Callan confirms "you wear skirts to just above the knee and not shorter if you want to be taken seriously".

Whatever the eventual choice, according to Ms Callan, "you can wear separates as long as they look right together, they're smart and they co ordinate".

Whereas most men really have no option but to wear a suit at work, women can opt for combining different pieces together.

"I tend to wear a dress and jacket," says Jean Wood. On the other hand, Mary Finan prefers suits, although not of an overtly masculine character. "Richard Lewis makes a lot of my suits and they're very feminine. I also think Armani's a beautiful tailor, and I like Sonia Rykiel, Calvin Klein and DKNY."

As for colour, Ms Finan says "it's horses for courses. I tend to wear neutrals - beige, black, navy and grey." Rose Callan, however, would "try not to wear dark shades. I think all navy and black is more suited to solicitors, so I go for greens, yellows, pinks and reds." Barbara Patton simply settles for "colours that I believe suit me. In summer I'd wear brighter shades and in winter darker ones".

What she and many other women propose is that practical considerations should be a priority when planning what to wear in the office. "Keep it simple," suggests Ms Patton. "Then it's easier to wear and easier to match."

Elaborate or overly fashionable clothes will draw unnecessary attention to the wearer and imply that concerns other than work are paramount. That's why men happily opt for the office uniform of a dark suit, shirt and tie; it's functional, universal and doesn't demand too much fuss or preparation.

Rose Callan says the clothes she typically wears for work have no place outside the office; "I'm much, much more casual the rest of the time - jeans and T shirts.

But as she points out, "you have to be smart in the office and give a sense of being a professional". The kind of unofficial but widely understood constraints which apply to men also serve for women at work.

Mary Finan emphasises this point, remarking "there's no differentials between the sexes. You have to look smart, with your clothes well cared for and well pressed. First impressions are extremely important. Carelessness in dress gives the impression of carelessness elsewhere."

So the ideal would seem to be an ensemble which is immaculate, yet doesn't draw too much attention to itself. Whether a suit or not, it will always include a jacket, tend towards single blocks of colour and all its elements will co ordinate.

Without being at the cutting edge of fashion, the office outfit can acknowledge changing trends and certainly ought to avoid dowdiness. Finally, it has to be comfortable, easy to wear and not demanding too much maintenance.

"You're at work to do a job and be of value to the company," explains Jean Wood. "Your clothes shouldn't be a distraction; they should be functional and allow you to get on with the main purpose of being in the office."