The might of the Scottish Rugby Union, Rangers and Celtic seems likely to be overtaken in the tartan popularity league by a new entry.

Husband and wife kiltmakers Geoffrey and Lorna Nicholsby, who already have the sporting trio in their stable, are now

official licensees, designers and weavers for a new fashion

challenge - the Rotary tartan.

''Home and abroad, orders and interest linked to the Glasgow convention are already among the largest we've ever handled. We anticipate an even greater flood of orders over the next few days,'' said Geoffrey Nicholsby, a member of a prominent Edinburgh kilt-making family.

He and his wife Lorna, a native of Glasgow, head Geoffrey (Tailor) Highland Crafts Ltd. In addition to its Scottish outlets it operates branches as far away as San Francisco and Atlanta.

''There is world-wide interest in the new Rotary tartan. We are even selling it on the Internet!'' The new tartan was introduced at last year's RI convention in Calgary. A visiting team of Rotarians and their wives, over from Glasgow to promote this year's Scottish event, appeared at all the Canadian events modelling clothes in the new tartan.

''The initial idea was to publicise the Scottish event, but the result also drew interest in the tartan - and orders - from delegates from scores of countries.

''The interest was enough to make us develop the design to a greater extent than we have ever tried any tartan before,'' said Geoffrey Nicholsby.

''For a start, we are weaving the cloth in three different weights including a lighter weight for ladies' wear. We are also producing it in polyviscous and in silk.

''The range of items being manufactured stretches from Highland wear to shirts and ties, from golf umbrellas to golf club covers, mugs and place mats - even baseball caps!''

Behind the enterprise, the story of the tartan concerned stretches over several years. The red, green and blue design is based on an original Glasgow District tartan, first recorded in 1819. Then, when Graeme Kidd, a city businessman and president-elect of Glasgow Rotary Club, first met the Scottish Tartan Society in l993 and asked their help in creating a special tartan for the l997 Glasgow convention, he was able to point out that the idea came from Glasgow Rotary Club, the first Rotary club in Scotland.

The Glasgow District tartan was considered then chosen, with the addition of an overlay of the Rotary colours of blue and gold. After some discussion with the board of Rotary International in the US, who initially blinked in surprise at the idea, the tartan was approved and registered

''The Glasgow convention may only last a few brief days, but we believe that interest in the official Rotary tartan will continue for many years,'' said Geoffrey Nicholsby. ''Our sales will certainly continue to benefit Rotary. A royalty on each and every sale will be divided between Rotary International and the Glasgow club.

''Customer interest is widespread and is by no means restricted to Rotarian families of Scottish descent who will be here for the convention. We have been producing thousands of yards of the tartan in its different weights to keep up with certain demand!''