For the diffident Swiss soldier -- help is at hand

Help is at hand for the bashful Swiss soldier who wants to be polite.

If he wishes to introduce himself to a certain young lady but can't quite think how to go about it, he may apply to surrogate letter writer Christian Roth of Hagglingen.

Then once he is out on a stroll with his new acquaintance, chances upon a friend, and wants to know the proper presentation, he can turn for guidance to a handy new Defense Ministry booklet.

Actually, Herr Roth's service is available to any man, not just to soldiers. (It's not available to women, since Herr Roth says he cannot properly project the feelings of the fair sex.) Similarly, the Swiss Defense Ministry's booklet of manners for soldiers has proved so popular with the general public that it was sold out at kiosks within days of its appearance.

Whether it's soldier or civilian who takes advantage of the counsel, the phenomenon suggests that some diffidence still survives this ultra-explicit age.

The diffidence in the village of Hagglingen is not only that of suitors who benefit from Herr Roth's letter-writing sensibilities. It's also manifest in Herr Roth himself, who is never in the mood to charge fees for his assistance after he has explored his clients' feelings sufficiently to compose an individualized valentine. He does accept chocolates, pralines, or an occasional gratuity for his ghostwriting. But this ''dreamer and romantic,'' as he calls himself, doesn't bill his customers, not even for the odd poem. He just enjoys his pseudonymous authorship, and depends for his livelihood on his profession as typesetter.

The diffidence of the Swiss Defense Ministry is perhaps more remarkable than Herr Roth's since military institutions are not noted for their devotion to politesse. It is not clear if the ministry was spurred to publish its booklet (''The Two Plus Two of Good Manners'' in the German edition, a more subtle ''24 Hours'' in French) by especially high standards in a neutral Army that has not seen battle in centuries - or by special dearths on the part of raw recruits.

Whatever its origins, the booklet is a smash hit. At 18 pages it can easily be tucked into a breast pocket for easy reference. With attractive brown-on-beige reproductions of 18th and 19th century prints of soldiers and dinner tables, it's pleasing to the eye. With boldface headings (''Ladies,'' ''Hands and Civilians,'' ''Among Equal Ranks,'' and ''Discretion Above All'') it gives quick answers.

Typical advice in these three categories reads:

''When a lady gives you her hand, you may take your cap off.'' ''It is up to the higher rank or the older person to offer his hand for a handshake.''

''If you are accompanying a higher officer and he meets an acquaintance and fails to introduce you right away, don't introduce yourself. Step back a bit and wait until you are 'noticed' or spoken to. (This also applies when you are on duty.)''

Other recommendations include finding the opportunity to wash the entire body thoroughly, even on maneuvers (''but use very fragrant oils with great restraint''); holding chairs for women to seat themselves at dinner, and apologizing for lateness. (In the latter situation the first rule reads, however , ''avoid lateness whenever possible.'')

Uniformed soldiers are further requested not to carry civilian packages, and especially not paper or plastic bags. They may, however, carry a woman's shopping parcels or umbrella. They may also offer their arm to their wives or women friends. Going downstairs they should always precede their women companions ''to be able to jump in and help in case of a fall.'' And of course in a restaurant they should always seat the lady with a view of the room ''(and not of the wall!)''

The complete Swiss soldier, it seems, is thoroughly instructed.